Poly(_(DL)-lactide-co-glycolice)(70:30) was synthesized from _(DL)-lactic acid and glycolic acid and The copolymers was made to micelles containing clonazepam for drug delivery system. The release experiments of the drug from micelles were operated at pH 7.4 phosphate buffer solution 37.0±0.05℃ and these results were as follows. The linearly-releasing time ranges of the drug from micelles prepared with the copolymers/drug weight ratio of 20:40, 20:20, and 40:20 (㎎ ) were 55, 45, and 33 days, respectively. So the linearly-releasing time of drug showed the order of micelles20/40 $gt; micelles20/20) micelles40/20. In short, the formulation allows polymeric micelles to suppress the burst effect of the drug release mechanism, which led to the controlled release pattern and the possibility of DDS for veinous injection.