Biodegradable poly(l-lactide) (PLLA)/octamethyl-polyhedral oligomeric silsesquioxanes (ome-POSS) nanocomposites were prepared via simple melt compounding at various ome-POSS loadings in this work. Scanning and transmission electron microscopy observations indicate that ome-POSS were homogeneously dispersed in the PLLA matrix. Effect of ome-POSS on the nonisothermal crystallization behavior, isothermal melt crystallization kinetics, spherulitic morphology, crystal structure, dynamic mechanical properties, and thermal stability of PLLA in the nanocomposites was investigated in detail. It is found that the presence of ome-POSS enhances both nonisothermal cold and melt crystallization of PLLA in the nanocomposites relative to neat PLLA. The overall isothermal melt crystallization rates are faster in the PLLA/ome-POSS nanocomposites than in neat PLLA and increase with increasing the ome-POSS loading; however, the crystallization mechanism of PLLA remains unchanged. The nucleation density of PLLA spherulites is enhanced, while the crystal structure of PLLA is not modified in the PLLA/ome-POSS nanocomposites. The storage modulus has been apparently improved in the PLLA/ome-POSS nanocomposites with respect to neat PLLA, whereas the glass-transition temperatures vary slightly between neat PLLA and the PLLA/ome-POSS nanocomposites. The thermal stability of PLLA matrix is reduced slightly in the PLLA/ome-POSS nanocomposites.