The nonisothermal crystallization behaviors of poly(lactic acid) (PLA) under ambient N-2 and compressed CO2 (5-50 bar) at cooling rates of 0.2-2.0 degrees C/min were carefully studied using high-pressure differential scanning calorimetry. The presence of compressed CO2 postponed. the crystallization peak to a lower temperature region while effectively reducing the half crystallization time and enhancing the crystallinity of the PLA specimen. On the basis of these findings, a new foaming strategy was proposed and utilized to fabricate PLA foams using the ordinary unmodified PIA. The upper and lower temperature limits of this foaming strategy, were 105 and 90 degrees C, which were determined by the melt strength and crystallization behavior of the unmodified PLA specimen, respectively. In this temperature range, PLA foams with interconnected structures, porosity of 67.9-91.4%, and expansion ratio of 15-30 times are controllably produced. The obtained PLA foams have widely distributed average bubble size of 80-270 mu m and CO2 enhanced crystallinity of 32-38%.