The high-profile design of ball and socket attachments lead to excessive occlusal vertical dimension which may has a bad effect on the muscle activity and also may lead to the denture breakage in completely edentulous patients. Therefore, will the use of locator attachment influence the muscle activity when compared to ball and socket attachment in mandibular implant overdenture? Aim: This RCT is to evaluate the activity of masticatory muscles of implant supported mandibular overdentures using two different types of attachments (ball and socket versus locator) in completely edentulous patients after insertion of attachments by two weeks, three months and six months. Methodology: The proposed number of the patients was 24, 12 per each group. The patients were divided into two groups: Group A: patients receive mandibular overdenture with ball & socket attachments Group B: patients receive mandibular overdenture with locator attachments Patients were be recalled 2 weeks later after attachment placement, 3 month and 6 month for muscle activity measuring using a digital electromyogram device Results: Implant retained mandibular overdentures with locator attachment system provide high muscle activity in comparison with implant retained mandibular overdentures with ball and socket attachment system. Conclusions: Implant retained mandibular overdentures with locator attachment system provide high muscle activity in comparison with implant retained mandibular overdentures with ball and socket attachment system. The muscle activity of masseter is higher than temporalis muscle and the activity of masseter and temporalis muscles increase with time.