The effects of incorporated amorphous poly(DL-lactide) (PDLLA) on the isothermal crystallization and spherulite growth of crystalline poly(L-lactide) (PLLA) and the structure of the PLLA/PDLLA blends were investigated in the crystallization temperature (T c ) range of 90-150 C. The differential scanning calorimetry results indicated that PLLA and PDLLA were phase-separated during crystallization. The smallangle X-ray scattering results revealed that for T c of 130 C, the long period associated with the lamellae stacks and the mean lamellar thickness values of pure PLLA and PLLA/PDLLA blend films did not depend on the PDLLA content. This finding is indicative of the fact that the coexisting PDLLA should have been excluded from the PLLA lamellae and inter-lamella regions during crystallization. The decrease in the spherulite growth rate and the increase in the disorder of spherulite morphology with an increase in PDLLA content strongly suggest that the presence of a very small amount of PDLLA chains in PLLA-rich phase disturbed the diffusion of PLLA chains to the growth sites of crystallites and the lamella orientation. However, the wide-angle X-ray scattering analysis indicated that the crystalline form of PLLA remained unvaried in the presence of PDLLA.