This study was conducted to compare clinically the retention of cobalt chromium and Acetal resin clasps in bilateral distal extensions cases. Ten partially edentulous patients were selected from the outpatient clinic of the Prosthodontic Department, Faculty of Oral and Dental Medicine. Cairo University, having bilateral distal extension edentulous areas (Kennedy class I) in the mandibular arch with the first or second premolar were the last standing teeth on the edentulous side. The ten patients were then divided into two equal groups , each group consists of five patients,Group 1: received partial denture with cobalt chromium clasps.Group 2: received partial denture with Acetal resin clasps. The retention of the partial denture was measured at the time of insertion ,after one month and lastly after three months have elapsed. Data was collected and the values of change between each successive time were tabulated and statistically analyzed. The result of the present study showed that there were no significant differences between the studied groups with regards to the retention values at the insertion visit (P-value >0.05) However, after one month of insertion there is a decrease in retention values in both studied groups but the Acetal is still un significantly higher than cobalt chromium(P-value >0.05). At the last visit the retention of Acetal was significantly higher than cobalt chromium (P-value <0.05), as mean of Acetal is 612 grams while mean of cobalt chromium is 583 grams.Conclusion: From the results of this study, it can be concluded that 1. Acetal resins offer the strength of metal, the flexibility and comfort of plastic, they make an ideal material for the fabrication of dental prosthesis, particularly clasps.2. Acetal is monomer free and offers an innovative and safe treatment alternative for patients who are allergic to conventional resins, also it can be used in periodontally compromised cases where minimum stresses onto the abutments are desired.3. Acetal resin offer a vastly expanded range of applications in removable partial dentures.