Effect of oxide layer formed on commercially pure titanium by heat-treatment on adhesion of serum proteins and differentiation activity of osteoblasts. Commercially pure titanium disks were polished and then heat-treated at 700°C for 30 minutes. Titanium oxide layer (rutile phase) was observed to form on the titanium disk surface after heat-treatment. The contact angle of a water droplet on the heat-treated titanium disk was about 14o while that of non-heat treated one was about 68o. The amount of adsorbed total serum protein on heat-treated titanium disk was four times higher than that on non-heat treated one. ALP activity of primary cultured mouse calvarial osteoblasts on heat-treated titanium disk was also higher than that on non-heat treated one with statistical significance of p < 0.05. It implies that the serum proteins preferentially adsorbed on titanium oxide layer formed on commercially pure titanium and it is likely to enhance the differentiation activity of primary cultured mouse cultured osteoblasts.