For reconstruction of the bony defect, various artificial substitutes were developed. Among them, there has been a study of calcium phosphate coated bone substitutes for increasing attachment of osteoblasts in vivo. The purpose of this study was to evaluate the effects of serum and platelet-rich plasma (PRP) on calcium phosphate coated culture plate for the initial attachment, proliferation and activity of osteoblasts. After sampling the blood from white rats and concentrating by centrifugation, the amount of attachment of PDGF-BB and TGF-beta on the calcium phosphate coated culture plate was measured. Cultured HOS and ROS 17/2.8 cell was measured on attachment level and proliferation rate of osteoblasts. Alkaline phosphatase activity of HOS and ROS 17/2.8 cell was measured for studying on the activating rate of osteoblast. 1. Counting the amount of platelets of seperated plasma and PRP, the average number of platelets was 177,003 cell/microliter in plasma, and 1,656,062 cell/microliter in PRP, which was about 9 times as high as in plasma. 2. Amount of PDGF-BB deposited at calcium phosphate coated plate had increased by the total amount of plasma and PRP on the culture plate, whereas TGF-betahad been deposited on the plate only when treated by 50microliter of PRP(p<0.01). 3. After plating serum and PRP for 3 hours, we attached with HOS and ROS17/2.8 cell for 1 hour and 4 hours. There were no significant difference of the attachment between serum and control group, whereas there were significantly difference of the attachment between depositioning of PRP and control group. 4. After attaching plasma and PRP for 3 hours, cell number has much increased when HOS and ROS17/2.8 cell had been cultured for 48 hours(p<0.05). 5. After attaching plasma and PRP for 3 hours, concentration of alkaline-phosphatase has increased when HOS and ROS17/2.8 cell had been cultured for 48 hours(p<0.01). These results suggested that PRP affected on initial cell attachment rather than proliferation and activation of osteoblasts at calcium phosphate coated plate.