Purpose: This study aimed to assess the change in the maximum bite force of completely edentulous patients rehabilitated with thermoplastic acrylic complete denture after placement of single implant-retained mandibular overdentures. Materials and Methods: Sixteen completely edentulous patients with age ranged from 50-60 years were selected from removable prosthodontic clinics, faculty of dental medicine, Al-Azhar University. Each patient received a thermoplastic acrylic complete denture. Three months after a new denture placement, bite force was evaluated using an occlusal force meter (GM10, Nagano Keiki, Japan). Each patient received a mid-symphyseal single dental implant, 10 mm length and 3.7mm diameter (Dentis, Dalseo-gu, Daegu , Korea) placed at the midline of the mandibular alveolar ridge. Two weeks after overdenture placement, bite force was evaluated to assess the changes in bite force after a single implant placement. Results: Bite force was increased considerably after single implant placement. It was significantly higher than the bite force recorded with a conventional thermoplastic complete denture. Conclusion: It was concluded that using immediate loading single implant-retained mandibular overdentures resulted in considerable improvement of bite force in completely edentulous patients.