The purpose of this study was to observe the effect of TGF-βl, which promotes differentiation and proliferation of osteoblasts, on bone regeneration. Experimental bone defects that measured 3 mm in diameter were created on the mandibles of guinea pig by removal of bone with the use of trephine burs. In one side of mandibular body, the experimental groups, bone defects were grafted with Biogran(Orthovita Co., U.S.A) and TGF-β1(R&D System Co., U.SA). In the remaining side of the mandiblar body, the control groups, bone defects were grafted with only Biogran. Guinea pigs in the control and experimental groups were serially terminated by fours on the 3 days, the 1 week, the 2 weeks, the 3 weeks, and the 4 weeks after experiment, and both sides of the mandibular bodies were removed and fixed with 10％ neutral formalin. They were decalcified and embedded in paraffin as using the usual method. The specimen sectioned and stained with hematoxylin and eosin. Also, they were radiographed with a soft X -ray apparatus. The obtained results were as follows; 1. Hemorrhagic condition, observed in the granulation tissues, disappeared on the 1 week after experiment in both groups, and more prominent in the experimental group. The granulation tissues of the experimental group had larger number of cells than those of the control group. 2. Osteoblastic differentiation in the margin of grafted material and adjacent bone was observed on the 1 week after experiment in both groups. Also, bone formation was observed in immature form on the 1 week after experiment. and more prominent in the experimental group. 3. In the polarizing microscopic examination, bone matrix was very loose on the 1 week after experiment, but increase in density with time, and more prominent in the experimental group. 4. In the microradiographic examination, newly formed bone was observed in the experimental group on the 2 weeks after experiment, and this was observed earlier than in the control group. Newly formed bone was increased with time and defected area was markedly decreased on the 4 weeks after experiment.