• Adjusted Mean Change From Baseline in Percent Predicted Morning PEF(%) During the 4-week Treatment Periods [ Time Frame: Crossover Period Weeks 1-4, 7-10 ] [ Designated as safety issue: No ]
• Adjusted Mean Change From Baseline in Percent Personal Best Morning PEF(%) During the 4-week Treatment Periods [ Time Frame: Crossover Period weeks 1-4, 7-10 ] [ Designated as safety issue: No ]
• Adjusted Mean Change From Baseline in Evening PEF During the 4-week Treatment Periods [ Time Frame: Crossover Period weeks 1-4, 7-10 ] [ Designated as safety issue: No ]
• Adjusted Mean Change From Baseline of Circadian Variation in Morning PEF(%) During the 4-week Treatment Periods [ Time Frame: Crossover Period Weeks 1-4, 7-10 ] [ Designated as safety issue: No ]
• Percentage of Subjects With Symptom-Free Nights & Days [ Time Frame: Crossover Period Week 1-4, 7-10 ] [ Designated as safety issue: No ]
• Percentage of Subjects With Rescue Medication-Free Nights and Days [ Time Frame: Crossover Period Weeks 1-4, 7-10 ] [ Designated as safety issue: No ]
• Adjusted Mean Change From Baseline in Morning PEF During the 20-week Extension Treatment Period [ Time Frame: Extension Period Weeks 11-30 ] [ Designated as safety issue: No ]
• Adjusted Mean Change From Baseline in Percent Predicted Morning PEF(%) During the 20-Week Extension Treatment Period [ Time Frame: Extension Period weeks 11-30 ] [ Designated as safety issue: No ]
• Adjusted Mean Change From Baseline in Percent Personal Best Morning PEF(%) During the 20-week Extension Treatment Period [ Time Frame: Extension Period weeks 11-30 ] [ Designated as safety issue: No ]
• Adjusted Mean Change From Baseline in Evening PEF During the 20-week Extension Treatment Period [ Time Frame: Extension Period weeks 11-30 ] [ Designated as safety issue: No ]
• Adjusted Mean Change From Baseline of Circadian Variation in PEF(%) During the 20-Week Extension Treatment Period [ Time Frame: Extension Period weeks 11-30 ] [ Designated as safety issue: No ]
• Percentage of Subjects With Symptom-Free Nights & Days After 20 Weeks of Treatment [ Time Frame: Extension Period Weeks 11-30 ] [ Designated as safety issue: No ]
• Percentage of Subjects With Rescue Medication-Free Nights & Days After 20 Weeks of Treatment [ Time Frame: Extension Period Weeks 11-30 ] [ Designated as safety issue: No ]

• Efficacy:
• Morning and evening PEF, Diurnal variation in PEF, Asthma symptoms, Rescue medication
• Safety:
• Adverse events, Clinical laboratory tests, Physical examinations, 12-lead ECG, Oropharyngeal test

To evaluate the efficacy and safety of GW815SF HFA MDI 25/50µg 1 inhalation bid in comparison with concomitant treatment with salmeterol xinafoate DPI 25µg 1 inhalation bid plus fluticasone propionate DPI 50µg 1 inhalation bid in paediatric patients with asthma.

To evaluate the safety of long-term treatment of GW815SF HFA MDI 25/50µg 1 inhalation bid in paediatric patients with asthma.

• Drug: GW815SF HFA MDI
• Drug: salmeterol and fluticasone propionate

• Active Comparator: SLM(salmeterol) 25mcg + FP(fluticasone propionate) 50mcg twice daily in first intervention period and SFC(salmeterol/fluticasone propionate) 25/50mcg twice daily in second intervention period and (after washout period).
• Active Comparator: SFC (Salmeterol/Fluticasone propionate combination) 25/50mcg twice daily in first intervention period and SLM (Salmeterol) 25mcg + FP (Fluticasone Propionate) 50mcg twice daily in second intervention period (after washout period).
• Experimental: SFC (salmeterol/fluticasone propionate combination) 25/50mcg twice daily in Extension period (after cross-over period).

Inclusion criteria:

• Inclusion Criteria for Entry in Run-in Period

A pediatric patient already diagnosed as having bronchial asthma who meets all of the following criteria is eligible for the study:

• Male or female patients aged ≥5 and ≤14 years. Enrolment of a female patient of childbearing potential is allowed only if she is tested negative in the pregnancy testing at the start of Treatment Period 1 and if she agrees to undergo pregnancy testing at the protocol-specified timings and to take contraceptive measures without fail.
• Written informed consent must be obtained from a legally acceptable representative of the subject. Consent of the subject him/herself should also be obtained, wherever possible, after giving an explanation in an as easy to understand as possible manner.
• An outpatient who has been treated with ICS (FP 100μg/day or equivalent) for at least 4 weeks prior to Visit 1.
• Able to use a peak flow meter in a correct manner in the investigator's/subinvestigator's judgment.
• Able to use MDI and DPI in a correct manner (with the assistance of his/her caregiver as necessary) in the investigator's/subinvestigator's judgment.

Inclusion Criteria for Entry in Treatment Period 1 A subject will be randomized to one of the two treatment groups only if he/she has completed the run-in period and meets all the following criteria.

1. Has a mean of morning PEF measurements in the last 7 days of the run-in period (excluding the first day of Treatment Period 1) ≤90% of his/her best PEF measurement .
2. Was able to perform entry in the asthma diary and PEF measurements in a correct manner in the investigator's/subinvestigator's judgment.
3. Able to use MDI and DPI in a correct manner (with the assistance of his/her caregiver as necessary) in the investigator's/subinvestigator's judgment.

Exclusion criteria:

• Exclusion Criteria for Entry in Run-in Period

A patient who applies any of the following criteria is not eligible for the study:

• Admitted to the hospital due to asthma exacerbation within 8 weeks prior to Visit 1.
• Used systemic steroid within 4 weeks prior to Visit 1.
• Received antibacterials or antivirals for treatment of upper or lower respiratory tract infection within 2 weeks prior to Visit 1.
• Has a safety problem in participation in the study because of a serious, uncontrolled systemic disease including nervous system disorder.
• Has or is suspected to have deep-seated mycosis or infection to which no effective antibacterial agent is available.
• Has or is suspected to have hypersensitivity to the investigational product, rescue medication or any ingredients of them.
• Is pregnant or lactating, may be pregnant, or plans for pregnancy during the study period.
• Has received the last dose in another clinical study within 2 months prior to this study.
• Is not eligible for the study in the investigator's/subinvestigator's judgment.

Exclusion Criteria for Entry in Treatment Period 1

Enrolment of a subject completing the run-in period into Treatment Period 1 will not be allowed if any of the following applies:

1. Admitted to the hospital due to asthma exacerbation during the run-in period.
2. Had upper or lower respiratory tract infection during the 2 weeks just before Visit 2.
3. Used prohibited drugs during the 2 weeks just before Visit 2.
4. Is not eligible for the study in the investigator's/subinvestigator's judgment.

Exclusion Criteria for Entry in Treatment Period 2

Enrolment of a subject completing the washout period into Treatment Period 2 will not be allowed if any of the following applies:

1. Admitted to the hospital due to asthma exacerbation during the washout period.
2. Had upper or lower respiratory tract infection during the 2 weeks just before Visit 4.
3. Used prohibited drugs during the 2 weeks just before Visit 4.
4. Is not eligible for entry in Treatment Period 2 in the investigator's/subinvestigator's judgment.