Purpose: was to compare the masticatory performance and maximum occlusal biting force for mandibular bilateral distal extension patients before and after removable partial denture rehabilitation to that of completely dentate individuals. Materials and methods: Ten partially edentulous patients with age ranged from (35-50) years. All patients had mandibular kennedy class I classification and completely dentulous maxillary arch. Each patient received a mandibular conventional removable partial denture. The electromyographic activity (EMG) and maximum bite force were evaluated for all patients before denture insertion then at delivery, after 2, 4 and 6 months respectively. Results: The results of this study showed that there were significant decrease in the electromyographic records while, there were significant increase in maximum bite force after denture insertion. Conclusion: Within the limitations of this study, the conclusions that could be obtained are that removable partial dentures improved patient's masticatory activity and maximum bite force which were better than prior to the constructions of prosthesis but these functions is usually improved to a lesser extent than that of the previous complete dentition.