Poly(D-,L-lactic acid) (PDLA) and PDLA-wood pulp fiber injection molded composites were modified with very small amounts (< 1 wt %) of N'-(o-phenylene)dimalemide and 2,2'-dithiobis(benzothiazole) by reactive extrusion and their resulting mechanical and thermal properties characterized. The modification produced an increase in the percent crystallinity (Xc), heat deflection temperature (HDT), impact energy, tensile strength, and modulus in PDLA. A significant reduction in the melting temperature (Tm) and an increase in the thermal resistance (Tmax) were also found. Fourier-Transform infrared spectroscopy (FTIR) suggests the creation of hydrogen bonds, a thiol ester and/or ester bond during the modification. Reactive extrusion of commercially available poly(lactic acid) (PLA) by means of N'-(o-phenylene)dimalemide and 2,2'-dithiobis(benzothiazole) provides a low cost and simple processing method for the enhancement of the properties of this biopolymer. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012