The effect of talc on the crystallinity and mechanical properties of a series of poly(lactic acid) (PLA)/talc composites has been investigated. The composites were prepared by melt blending followed by compression molding. It was found that talc acted as a nucleating agent and increased the crystallinity of the PLA from 2% to 25%. There was significant improvement in Young's modulus of the composites with increasing talc addition and these results were found to fit the Halpin Tsai model. Thermo-mechanical tests confirmed that the combination of increased crystallinity and storage modulus leads to improvement in the heat distortion properties. POLYM. ENG. SCI., 54:64-70, 2014. (c) 2013 Society of Plastics Engineers