Effect of the coexistence of carbon nanotubes (CNTs) and shear flow on the crystallization of injection-molded poly(L-lactic acid) (PLLA) was explored in the present work. The wide-angle X-ray diffraction (WAXD) results show that CNTs increases the crystallinity of injection-molded PLLA with the mold temperature set at 40 or 80ºC, due to its nucleation effect. However, CNTs decreases the crystallinity of PLLA with the mold temperature 100ºC. Meanwhile, shear flow promotes the crystallization of PLLA significantly. For the coexistence of CNTs and shear flow, shear flow promotes the crystallization so significantly that the nucleation effect of CNTs is negligible. On the contrary, CNTs decreases the crystallinity of PLLA with the application of shear flow field. The reason why CNTs plays different roles in the crystallization of injection-molded PLLA under different processing condition was studied by differential scanning calorimeter (DSC). The DSC and WAXD results indicate that CNTs promotes the crystallization of PLLA under the processing condition unfavorable for the crystallization of neat PLLA, such as high supercooling or lacking of shear flow. However, under the proper mold temperature or/and shear flow favorable for the crystallization of PLLA, CNTs decreases the maximum achievable crystallinity resulting from the restriction of chain motion or crystal disruption. The thermal property of the samples was also studied by dynamic mechanical analysis (DMA) and vicat softening temperature (VST), indicating that CNTs or/and shear flow increase storage modulus especially above the glass transition temperature and increase greatly the VST of PLLA due to the promotion of crystallization with the mold temperature 40 and 80ºC, respectively. Keywords: poly(L-lactic acid), crystallization, carbon nanotubes, shear flow, injection-molding. Acknowledgments: This study is supported by the National Natural Science of China (Grant NO. 51120135002, 51473101).