Multi-walled carbon nanotube (CNT) grafted poly(L-lactide)-block-poly(D-lactide) copolymer (CNT-L-D) was synthesized and incorporated into a equimolar high-molecular-weight poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) blend to study its effect on the stereocomplex crystal formation of PLLA and PDLA. The ternary blends were prepared by casting polymer solutions of CNT-L-D, PLLA, and PDLA with different compositions. The nonisothermal and isothermal melt crystallization of CNT-L-D, PLLA/PDLA/CNT-L-D blends were investigated by differential scanning calorimetry, wide-angle X-ray diffraction and optical microscopic observation. With the addition of CNT-L-D, the stereocomplex crystallization in ternary blends is driven to a higher degree, while the homocrystallization is suppressed. Sc crystallites formed exclusively in the blend with 10 wt% CNT-L-D in both isothermal and nonisothermal melt crystallization. Consequently, it is revealed that CNT-L-D can work as an effective nucleating agent to improve the sc formation ability in the equimolar high-molecular-weight PLLA and PDLA blends.