To examine the formation of a new bone using various metal implants, 316L stainless steel, Co–Cr–Mo casting alloy, and Ti–6Al–4V and Ti–15Zr–4Nb–4Ta alloys were implanted into the rat femur and tibia for up to 48 weeks. Morphometrical parameters, namely, new bone formation rate, bone contact rate, new bone thickness and osteoid formation rate were investigated. Although a thin osteoid layer in a new bone-metal interface was observed in all the alloy implants, a new bone was well formed around all the alloy implants in the bone marrow of the rat femur and tibia up to 48 weeks. Neither the resorption of bone nor inflammatory reactions such as the presence of foreign-body giant cells and infiltration of inflammatory cells were also evident in the histological examination of these implants. A normal bone remodeling was observed in the new bone-metal implant interface, and osteoblasts capable of differentiating into a new bone tissue were lined on the implant side in the new bone-metal implant interface. Many osteocytes were observed in the lamellar bone tissue. The new bone formed around all the alloy implants developed into a calcified bone consisting of lamellar structure with increasing implantation period. A capsulated fibrous connective tissue was observed in the 316L stainless steel and Co–Cr–Mo alloy implants at 48 weeks after long-term implantation. Many osteoclasts were observed at the interface between the fibrous connective tissue and lamellar bone tissue. The bone formation rates around all the alloy implants were markedly high, approximately more than 90% at 4 weeks after implantation, and thereafter, no marked change was observed. The bone contact rate of Co–Cr–Mo alloy implant was slightly higher than that of 316L stainless steel implant. In the early stage of implantation (4–12 weeks), the bone contact rates of Ti alloy implants were significantly higher than that of Co–Cr–Mo alloy implant. In the late stage of implantation (24–48 weeks), the osteoid formation rates of Co–Cr–Mo and Ti–6Al–4V alloy implants tended to increase, but not significantly. Significant differences in the bone morphometrical parameters, suggesting osteocompatibility, were detected, although histological findings were not evident. Histological examinations of undecalcified sections were essential for confirming the interface between a newly formed bone and a metal implant, and morphometrical parameters, suggested to be good markers of osteocompatibility for the investigation of various metal implants.