Objective: To evaluate the clinical effect and masticatory performance of two early loaded small diameter implants(SDI)retained mandibular overdentures.Material and method: Eight mandibular edentulous patients received two SDIs(3.25mm or 2.2mm,ERA Mini Dental,Zimmer Dental Inc.)insertion between the mental foramina.The mandibular overdentures were connected with implants for early loading in the period of 2-4 weeks following implant insertion.The clinical and X-ray examination were conducted at ten days,three months,six months and one year after surgery.Data of Oral Health Impact Profile-20E(OHIP-20E)and Visual Analogue Scale(VAS)were collected at baseline,two weeks,three months,six months and one year following overdenture loading.Masticatory efficiency was evaluated before surgery and at six months after overdenture loading.