This study has been performed to evaluate the relationship between the remained mineral components in a decalcified bone matrix and an ectopic bone formation efficiency. The freezed rat diaphyseal cortical bones measuring 0.5cm in length were demineralized in heated 0.6N HC1 at 60degrees C for 5,10,15,20,25,30,35,40, minutes, respectively, using a controlled heat ultrasonic cleaner. Each 1cc of decalcifying soultion taken during decalcification procedure was used to calculate calcium content using calcium dignostics kit under 600nm of spectrophotomer. After decalcification, each specimen was also weighed. Then each prepared specimen was implanted into the dorsal pouch of 24 Sprague-Dawley rats divided into 8 groups by time course. The implants were harvested at 1,2, and 3 weeks and prepared for routine H-E stain specimens to evaluate osteogenic activity. The results are as follows: 1. Tgere was statistical significant difference in change of calcium concentrtion up to demineralization of 30 minutes and each allogenic bones decalcifed up to 20 minutes revealed 99.65% of decalcification in average. 2. There was statistical significant difference in change of weight in demineralized allogenic bone up to 20 minutes treatment but, no significant change was noted after that time. 3. the histologic analysis revealed active ecotopic bone formation in the implanted allografts demineralized for 20, 25, 30, minutes, respectively. However, the other groups of allografts showed relatively poor osteoinductive activity. These findings suggest that complete decalcification with a minimized degeneration of collegen matrix is nesessary to induce maximal osteogenesis by decalcified bone allograft.