The aim of this study was to evaluate by finite element analysis influence of investigated expanding implant on stress distribution and to observe biocompatibility, bone formation feature and change in the bone contact area around the expanding implant through experimental animal study. FEA models of the mandible were constructed based on three-dimensional graphic data of the bone structure around an osseointegrated implant, analysis of stress distribution followed by 100N vertical, 50N horizontal was done. And in the animal study, expanding implant were placed in the mandibles of eight Korean mongrel dogs and analyzed the results with histomorphometric measurements. In finite element analysis, compressive stresses are produced at the bone tissue surrounding the implant, and the contact area between the implant and the bone tissue is increased, which result in increased resistance to horizontal and vertical pressure loads. In the histomorphometric analysis, the measured ratio of the contact surface and bon desity between implant and bone was similar to those of the controlled group from 6 weeks. It is thought that increased horizontal and vertical resistance is a great help to the immediate loading on expanding implant and that there needs standardizing quantitative measurement of implant stability and osseointegration to determine whether or not to use the functional loading and to reduce the total treatment period reliably by placing functional loading on each implant based on both bone quality and implant stability.