Novel nanocomposites from poly(L-lactide) (PLLA) and an organically modified layered double hydroxide (LDH) were prepared using the melt-mixing technique. The structure and crystallization behavior of these nanocomposites were investigated by means of wide-angle X-ray diffraction (WAXD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and polarized optical microscopy (POM). WAXD results indicate that the layer distance of dodecyl sulfate-modified LDH (LDH-DS) is increased in the PLLA/LDH composites, compared with the organically modified LDH. TEM analysis suggests that the most LDH-DS layers disperse homogenously in the PLLA matrix in the nanometer scale with the intercalated or exfoliated structures. It was found that the incorporation of LDH-DS has little or no discernable effect on the crystalline structure as well as the melting behavior of PLLA. However, the crystallization rate of PLLA increases with the addition of LDH-DS. With the incorporation of 2.5 wt % LDH-DS, the PLLA crystallization can be finished during the cooling process at 5 degrees C/min. With the addition of 5 wt % LDH-DS, the half-times of isothermal melt-crystallization of PLLA at 100 and 120 degrees C reduce to 44.4% and 57.0% of those of the neat PLLA, respectively. POM observation shows that the nucleation density increases and the spherulite size of PLLA reduces distinctly with the presence of LDH-DS. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2222-2233, 2008