Purpose: To assess the effect of two attachment systems ball and socket and locator attachments and two occlusal patterns; bilateral balanced and monoplane occlusion on the electromyographic activity of temporalis and masseter muscles in mandibular implant retained overdenture. Material and Methods: Twelve male completely edentulous patients were selected from the outpatient clinic, Prosthodontic department, Faculty of Dental Medicine for Girls, Al-Azhar University. The patients were divided into two different groups: Group I received the Locator attachment and Group II received ball and socket attachment. All patients in both groups were divided equally into two subgroups: In subgroup 1: Patients received complete dentures with bilateral occlusal pattern and subgroup 2 the patients received complete denture with monoplane occlusion. Electromyographic activity for masseter and temporalis muscles were made after one month and three months for soft food and hard food. In subgroup 1 the dentures were replaced by the dentures with monoplane occlusion while in subgroup 2 the dentures were replaced by the denture with bilateral balanced occlusion. In group I and II attachments were switched and the same steps were followed for subgroups. The data were collected. Results: When using denture with bilateral balanced occlusion with locator attachment showed low electromyographic activity on the masseter and temporalis muscle than the denture with monoplane occlusion and there was no significant difference when using soft food during the first month while after 3 months there were significant difference. When using ball & socket attachments there were significant difference when using soft and hard food when using hard food there are significant difference between the subgroups. Conclusion: The two implant retained mandibular overdenture with the locator attachment showed relatively low electromyographic activity of the masticatory muscles (masseter and temporalis) than with ball and socket attachment and high electromyographic activity of the masticatory muscles (masseter and temporalis) with monoplane occlusion than with bilateral balanced occlusion.