The isothermal crystallization behavior of -cellulose short-fiber reinforced poly(lactic acid) composites (PLA/-cellulose) was examined using a differential scanning calorimeter and a petrographic microscope. Incorporating a natural micro-sized cellulose filler increased the spherulite growth rate of the PLA from 3.35 m/min for neat PLA at 105 degrees C to a maximum of 5.52 m/min for the 4 wt % PLA/-cellulose composite at 105 degrees C. In addition, the inclusion of -cellulose significantly increased the crystallinities of the PLA/-cellulose composites. The crystallinities for the PLA/-cellulose composites that crystallized at 125 degrees C were 48-58%, higher than that of the neat PLA for approximate to 13.5-37.2%. The Avrami exponent n values for the neat and PLA/-cellulose composites ranged from 2.50 to 2.81 and from 2.45 to 3.44, respectively, and the crystallization rates K of the PLA/-cellulose composites were higher than those of the neat PLA. The activation energies of crystallization for the PLA/-cellulose composites were higher than that of the neat PLA. The inclusion of -cellulose imparted more nucleating sites to the PLA polymer. Therefore, it was necessary to release additional energy and initiate molecular deposition. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013