POIY(L-lactic acid) (PLA) filaments were spun by melt-spinning at 500 and 1850 mm(-1), and further drawn and heat-set to modify the morphology of these PLA filaments. PLA yarns were characterized by wide-angle Xray diffraction (WAXD) and sonic method. WAXD reveals that PLA yarns spun at 500 mm(-1) are almost amorphous while the PLA filaments spun at 1850 mm(-1) have about 6% crystallinity. This is different from PET filaments spun at the same speed that have almost no crystallinity. Both drawn and heat-set PLA filaments showed much higher crystallinity (60%) than do as-spun fibers produced at 500 and 1850 mm-1 speed, which is also higher than the usual heat-set PET yarns. It appears that crystalline orientation rapidly reaches a value in the order of 0.95 at 1850 mm(-1) and that drawn- and heat-set yarns have almost the same crystalline orientation values. Molecular orientation is relatively low for as-spun PLA yarn, and molecular orientation increased to similar to 0.5 after drawing or heat-setting or both. (c) 2006 Wiley Periodicals, Inc.