The purpose of this study was to compare the effectiveness of soft occlusal splint therapy on the electromyographic activity of masticatory muscles (ateriors temporalis and masseter) before and after the application of a muscle relaxation splint. Electromyography recordings from the masseter and anterior temporalis muscles were analyzed quantitatively during maximal clench, rest and mastication usual, before and after the treatment without a splint. Ten patients whose chief complaint was Temporomandibular Disorders (TMD) were selected for the study. After the initial evaluations soft occlusal splints (muscle relaxation splints) were applied, and the patients were instructed to use the splints for four weeks. Surface electromyographic recordings were taken from each patient, as clinical evaluations of TMD (Index of Helkimo), both evaluations before the beginning of clinical therapy and after four weeks of wearing splints. The data obtained were analyzed by Wilcoxon´s and Friedman´s tests.