Biodegradable poly(L-lactide) (PLLA)/multiwalled carbon nanotubes (MWNTs) nanocomposites were prepared via solution blending using two kinds of MWNTs, i.e., pristine multiwalled carbon nanotubes (p-MWNTs) and carboxyl-functionalized multiwalled carbon nanotubes (f-MWNTs). Various techniques were used to investigate the functionalization of MWNTs on the morphology, crystallization, and hydrolytic degradation of PLLA in the nanocomposites. Both MWNTs show fine dispersion in the PLLA matrix; however, the dispersion of f-MWNTs is better than that of p-MWNTs. The incorporation of MWNTs accelerates the crystallization of PLLA in the nanocomposites due to the heterogeneous nucleation effect; furthermore, the crystallization rate of PLLA is faster in the PLLA/f-MWNTs nanocomposite than in the PLLA/p-MWNTs nanocomposite. The exciting aspect of this research is that the hydrolytic degradation of PLLA is enhanced after nanocomposites preparation.