Objective: The objective of this in vivo study was done to evaluate the biting force when restoring the edentulous mandible with an implant supported overdenture using two conventional implants or two mini implants.  Subjects and Methods: Sixteen patients were selected for this study free from any systemic disease or local factor that contraindicate implant placement. Patients were divided into two equal groups: In group I (control group) each patient had received a two conventional implant in the mandible and in group II (test group) each patient had received two mini implant in the mandible. Implants were placed using flapless surgery and immediately loaded by picking up the metal house into the denture. Assessment of bite force was done by force sensor. The evaluation was done at 1 week, and at 3, 6, 9, 12 months. Results: The results showed that the control group had statistically significant higher values of the bite force than the test group.  Conclusions: Mandibular implant supported overdenture by two mini implants have shown less retention, biting force, and masticatory efficacy than the overdenture supported by two conventional implants.