The aim of this randomized clinical trial was to evaluate marginal bone changes related to CAD/CAM metallic and PEEK partial denture frameworks in mandibular Kennedy class I Materials and methods: 24 patients with mandibular Kennedy class I were randomly assigned into two groups treated either with CAD/CAM PEEK or cobalt –chromium PDs. Bone height changes were assessed using standardized digital periapical radiographs with paralleling technique at baseline, 3 and 6 months. Result: The marginal bone height changes values of PEEK frameworks group were lower than that of the metallic frameworks group, but the difference was statistically insignificant throughout the follow up periods and between groups. Conclusion: CAD/CAM PEEK Partial dentures showed more favorable effect on abutment teeth than CAD/CAM metallic partial dentures. However, more clinical studies are still needed to evaluate its long term effect.