Background: Implant supported overdentures are a widely-accepted treatment approach with long-term effectiveness for restoring function and aesthetics, as well as improving masticatory efficiency and individual satisfaction. Recently, Computer aided design-Computer aided manufacturing (CAD/CAM) fabricated bars are increasingly used providing high stability levels, a stress-free fit, and high precision level. Objective: to evaluate the crestal bone height surrounding the implants in implant-supported mandibular overdentures retained with CAD/CAM milled Co-Cr and PEEK bar attachments using CBCT. Materials and Methods: Twenty completely edentulous patients were selected from the outpatient clinic, Prosthodontic Department, Faculty of Dentistry, Ain Shams University. They were classified into two groups: Group I: Ten patients received CAD/CAM milled Co-Cr bar supporting implant mandibular overdenture. Group II: Ten patients received CAD/CAM milled PEEK bar supporting implant mandibular overdenture. Radiographic evaluation using CBCT was carried out at insertion time, six months, and twelve months after loading to evaluate the marginal bone height changes around the implants in both groups. Results: Statistical analysis of the data revealed significant increase in the amount of bone loss around the implants for group I (Co-Cr) compared to group II (PEEK) during the one year follow-up period. Conclusion:The use of CAD/CAM milled Co-Cr and PEEK bar attachments to support implant mandibular overdenture meets the implant success criteria based on clinical and radiological findings after one year. However, CAD/CAM milled PEEK bar may be advantageous than CAD/CAM milled Co-Cr bar in terms of reduced bone loss.