Acid-oxidized multiwalled carbon nanotubes (A-MWCNTs) with a range of reduced aspect ratios (from about 11 to 5.8) were obtained by acid oxidization of MWCNTs in the mixture of HNO 3 and H 2 SO 4 for varying periods of 1, 3, 8 and 12 h, respec- tively. The aspect ratios and surface functionalization of A-MWCNTs were well characterized by scanning electron microsco- py (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and thermogravimetric analysis (TGA). Poly(L-lactide)/A-MWCNT composites containing 0.5 wt% A-MWCNTs with a range of reduced aspect ratios were prepared by solution cast. The effects of added A-MWCNTs on the isothermal crystallization kinetics of poly(L-lactide)/A-MWCNT composites were investigated by means of differential scanning calorimetry (DSC), rheology and polarized optical microscopy (POM). It is surprising to find that not only the addition of A-MWCNTs effectively increases the poly(L-lactide) (PLA) crys- tallization kinetics, but also the nucleation ability of A-MWCNTs for PLA crystallization exponentially increases with the re- duced aspect ratio, that is to say, those with lower aspect ratios show much stronger nucleation ability for PLA crystallization than those with higher aspect ratios. The exponentially increased nucleation ability of A-MWCNTs with a range of reduced aspect ratios for PLA crystallization is disclosed. Acid-oxidized multiwalled carbon nanotubes (A-MWCNTs) with a range of reduced aspect ratios (from about 11 to 5.8) were obtained by acid oxidization of MWCNTs in the mixture of HNO 3 and H 2 SO 4 for varying periods of 1, 3 , 8 and 12 h, respec- tively. The aspect ratios and surface functionalization of A-MWCNTs were well characterized by scanning electron microsco-py (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and thermogravimetric analysis (TGA). Poly (L-lactide) / A-MWCNT composites containing 0.5 wt% A-MWCNTs with a range of reduced aspect ratios were prepared by solution cast. The effects of added A-MWCNTs on the isothermal crystallization kinetics of poly (L-lactide) / A-MWCNT composites were investigated by means of differential scanning calorimetry (DSC), rheology and polarized optical microscopy (POM). It is surprising to find that not only the addition of A-MWCNTs actually increases the poly (L-lactide) ( PLA) crys- tallization kinetics, but also the nucleation ability of A-MWCNTs for PLA crystallization exponentially increases with the re- duced aspect ratio, that is to say, those with lower aspect ratios show much stronger nucleation ability than PLA with those with higher aspect ratios. The exponentially increased nucleation ability of A-MWCNTs with a range of reduced aspect ratios for PLA crystallization is disclosed.