Objective To evaluate the bone regenerative potential of reconbinant human bone morphogenetic protein 2(rhBMP-2) / collagen on adult rat calvarial bone. Methods A tight subperiosteal pocket was produced under both sides ofthe temporal muscle in rats. rhBMP-2 / collagen was implanted in one side and collagen alone was implanted in the other side as control. The rats were sacrificed 2, 4 and 8 weeks after operation. The specimen was harvested and examined histologically. For morphometric analysis, the thickness of the temporal bone of both sides was measured and compared. Results The rhBMP-2 / collagen onlay implant resulted in active bone formation and the augmented bone was connected directly with the original bone, whereas the collagen alone resulted in neither bone nor cartilage production. The ossification process in the rhBMP-2 / collagen occurred directly through bone formation, similar to intramembranous ossification. Conclusion rhBMP-2 / collagen is an effective material as a biological onlay implant.