The ultimate goal of periodontal therapy is promoting the regeneration of lost periodontal tissue. The purpose of this study is to evaluate the effect of treatment using decalcified freeze dried bone allograft as a bone graft material. 47 intrabony defects from 27 patients with clinical diagnosis of chronic periodontitis were selected among those 24 defects were treated via flap operation only and designated as the control group, the other 23 defects were treated with decalcified freeze dired bone allografting via flap operation and designated as the experimental group. Clinical parameters including probing depth, loss of attachment, probing bone level and gingival recession have been recorded at 6th months, and the significance of the changes has been analyzed. The results are as follows : 1. Probing depths were reduced significantly in both control group($2.75{pm}0.99mm$) and experimental group($3.69{pm}0.97mm$) postoperatively(p<0.01). Experimental group showed significantly higher decrease compared to the control group(p]0.01). 2. Loss of attachment showed statistically significant decrease in both control group($1.77{pm}1.08mm$) and experimental group postoperatively($2.70{pm}1.55mm$). Experimental group showed significantly higher decrease compared to the control group(p]0.05). 3. Probing bone levels were reduced with statistically significance in both control group($1.08{pm}0.97mm$) and experimental group($4.00{pm}1.41mm$) postoperatively(p<0.01). Experimental group showed significantly higher decrease compared to the control group(p<0.01). 4. Gingival recession showed statistically significant increase in the control group($1.21{pm}0.72mm$) and experimental group($1.00{pm}1.09mm$) postoperatively(p<0.01). There was no statistical significance between the control group and the experimental group. On the basis of these results, treatment using allogenic decalcified freeze dried bone is effective in reducing probing depth, loss of attachment and probing bone level. Therefore allogenic decalcified freeze dried bone is an effective bone graft material in periodontal regeneration.