Ten unilateral partially edentulous patients opposing maxillary completely dentitions were selected from the outpatient clinic of the prosthodontics department, Faculty of Oral and Dental Medicine, Cairo University. The patients were divided into two situations according to the type of direct retainer: Situation I: Class II Kennedy classification restored with removable partial denture with clasps on the principle abutments. Situation II: Class II Kennedy classification restored with removable partial denture with extra coronal attachments on the principle abutment. The study was designed to compare the effect of using clasps versus extra coronal attachments retained removable partial denture in unilateral mandibular distal extension edentulous area (Kennedy Class ΙΙ) on muscle activity of temporalis and masseter muscles. Activity of the masseter and temporalis was recorded by the cadwel Excel high power EMG/EP instrument At first patient was received clasp retained partial denture. Muscle activity of temporalis and masseter muscles were recorded immediately after prosthesis insertion, one week, and then after one month following insertion. After the last record was taken the patients were left for a month without denture for muscular relief till attachment retained partial denture was constructed. After patient received attachment retained partial denture was constructed the muscle activity of temporalis and masseter muscles were recorded same periods as clasps situation. The data collected and statistically analyzed. Conclusion: From the result obtained the following was concluded: • Increase in the EMG muscle activity during follow up period after construction of clasp retained partial denture and attachment retained partial denture for temporalis and masseter muscles. • Percent change in muscle activity was higher in clasp retained partial denture than attachment retained partial denture.