Purpose: The aim of this study was to evaluate implant stability in single implant versus two implant mandibular over-denture of completely edentulous patients. Materials and methods: twenty four completely edentulous patients were divided randomly into two groups, intervention Group received single implant supported overdenture, while the conventional group received two implant supported over denture. Osstell device was used to measure implant stability. Implant stability was measured equally for the two groups. At first primary stability was measured at time of implant insertion after that secondary implant stability was measured every three months up to nine monthResults: Comparing the two groups during the whole study period, the results demonstrated that no differences in implant stability between two groups. (P value < 0.05) Conclusion Regarding initial and delayed implant stability, Minor changes were observed between the two groups during the whole follow up periods. Implant stability of single implant supported over denture is closer to two implant supported over denture