Background: Posterior distal extension partial denture present a number of design challenges. Especially the equitable distribution of forces that may become adverse during functional and parafunctional activities. So to maintain remaining alveolar ridges and teeth in an optimal state of health and to provide the patient with improved comfort and function, these forces are often compensated for to some extent by framework and denture base design variation. Purpose: The aim of this study was to evaluate the quality of life and muscle activity for patients restored by mandibular distal extension removable partial dentures (MDERPD) that retained either by CAD-CAM designed telescopic crown retainers or CAD-CAM designed conventional clasp. Materials and Methods: 42 partially edentulous patients were selected and randomly allocated into two identical groups. Group (1) Received a (MDERPD) retained with CAD-CAM designed telescopic crown retainers. Group (2) Received a (MDERPD) retained with CAD-CAM designedconventional clasp. Each group evaluated as regarding the quality of life through the Arabic version of OHIP-EDENT questionnaire. The digital electromyography (EMG) is used to record the muscle activity of anterior temporalis and masseter muscles. Conclusion: CAD-CAM designed telescopic crown retained RPD improved the quality of life and muscle activity of partially edentulous patients more than CAD-CAM designed clasp retained RPD.