The effects of fillers on the crystal formation and crystalline structure of poly(lactic acid) (PLA) are unclear. In this study microfibrillated cellulose (MFC) was used as filler to compound with PLA and the crystallization behavior of PLA/MFC composites was investigated. The crystallization process of PLA/MFC composites was observed by wide angle X-ray diffraction (WAXD) and differential scanning calorimeter (DSC) synchronously to investigate the effect of MFC on the formation of crystal and evolvement of crystalline structure of PLA. Results showed that MFC enhanced the crystallization rate drastically, but had no much influence on the crystal form of PLA when isothermally crystallized at different temperature. However, different crystal forms of PLA were obtained respectively from the pure PLA and PLA/MFC composites during the same cooling process. Detailed analysis indicated that the primary cause for the phenomenon was the enhancement of the crystallization temperature of PLA due to the addition of MFC. (C) 2013 Elsevier Ltd. All rights reserved.