the present invention provides a direct polycondensation method for medical biodegradable polylactic acid using creatinine catalyzed lactic acid . the invention uses commercialized creatinine in human body ) as the catalyst and industrial lactic acid as the monomer to synthesize the high biosafety of medical pla in terms of second polycondensation without solvent . instead of tin catalysts having cytotoxicity , the catalyst used in the invention has high biocompatibility and biosafety . the synthesized pla does not contain any metal and other toxic components ; therefore , it can be used as the carrier for targeting drugs and controlled release drugs . in addition , the green catalyst and green processing method are used in the invention to synthesize the green biodegradable pla with high biosafety . the polymerization reaction is simple and the raw materials required are low in costs , thus it is easy for industrialization . further , the molecular weight distribution for all synthesized products is narrow and the molecular weight is controllable within 1 . 5 - 3 . 0 × 10 4 .