Poly((D,L)-lactide) with a molar mass of 105 g. mol(-1) and a yield over 90% was produced in 10 min by the ring-opening polymerization Of (D,L)-lactide under microwave irradiation with forward power of 255 W. A degradation of the Poly((D,L)-lactide) was also induced by microwaves with a power level over 340 W. The molar mass of Poly((D,L)-lactide) was dependent upon the competition between the polymerization of (D,L)-lactide and the degradation of the resulting polymer.