The puroose:The aim of this study was to evaluate the effect of different designs of removable partial denture (RPD) supported with distal implant for the treatment of mandibular Kennedy class II cases on the behavior of oral structures by using Three-dimensional (3D) finite-element analysis (FEA). Materials and methods: A three models of mandibular class II Kennedy arch received three RPD designs were evaluated. The first model involves the use of RPI clasp on the first premolar. The second model involves the use of an extra coronal attachment at the distal aspect of the splinted first bicuspid and canine abutments. The third model received a bilateral (RPD) with RPI clasp on the first premolar and a double Aker clasp on the second premolar and first molar of the opposite side. For all models a single implant was placed at the second molar region with a conventional ball and socket attachment. For each model, a vertical and oblique loads of 100N were applied to the second molar area . The created model components were then imported to FEA software (ANSYS). Results: The first model recorded a significant less stresses at the bone, mucosa and abutment teeth in comparison to the other models but insignificance differences occurred in the total deformations. Conclusion: The von Mises stress and deformation produced in case of model 1 (clasp design) was better than that occurred with the other two models ( bilateral and extracoronal attachments)