To study the effect of organophilic clay concentration on nonisothermal crystallization, poly(L-lactic acid) (PLLA)/montmorillonite (MMT) nanocomposites were prepared by mixing various amounts of commercial MMT (Cloisite(R) 30B) and PLLA. The effect of MMT content on melting behavior and crystal structure of nonisothermal crystallized PLLA/MMT nanocomposites was investigated by differential scanning calorimetry (DSC), small-angle X-ray scattering, and wide-angle X-ray diffraction (XRD) analyses. The study was focused on the effect of the filler concentration on thermal and structural properties of the nonisothermally crystallized nanocomposite PLLA/MMT. The results obtained have shown that at filler loadings higher than 3 wt %, intercalation of the clay is observed. At lower clay concentrations (13 wt %), exfoliation predominates. DSC and XRD analysis data show that the crystallinity of PLLA/MMT composites increases drastically at high clay loadings (59 wt %). In these nanocomposites, PLLA crystallizes nonisothermally in an orthorhombic crystal structure, assigned to the a form of PLLA. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012