Purpose: The aim of the research was to evaluate the masticatory muscle performance with different resilient denture base materials in maxillary single denture. Material and methods: Six patients were included in this cross over study. In the first stage of the study, the patients were instructed to use the denture (PMMA denture base) for 1 month and the masticatory muscle activity was assessed in the second and fourth weeks after delivery. A wash out period of two weeks was applied in this study to eliminate the effect of the previous denture then the denture material was relined to soft liner, then replaced with breflex flexible material. For each type of denture base relining material, EMG was recorded after 2 weeks form day of denture insertion (adjustment phase) then EMG was recorded after 4 weeks after complete muscles adaptation (adaptation phase). Results: Comparison between three types of denture bases was performed by one way ANOVA test which revealed significant difference between them regarding duration and amplitude of both masseter and temporalis after 2 weeks and after 4 weeks as P <0.05. Conclusion: This in-vivo study, which shows that rehabilitation of correct masticatory muscle function, improved with the proper use of denture base material and which leads to improvement in the patient's quality of life.