Monomer casting polyamide 6(MCPA6)/toluene 2,4-diisocyanate functionalized multi-walled carbon nanotubes (MWNTs-NCO) nanocomposites were prepared via in situ anionic ring opening polymerization, and the non-isothermal crystallization behavior of the nanocomposites were investigated by differential scanning calorimetry with various cooling rates. The commonly used Avrami, Ozawa, Mo, and Urbanovici-Segal models were employed to analyze the non-isothermal crystallization data and the validity of the models on the process of MCPA6 and its nanocomposites was discussed, where Mo and Urbanovici-Segal models could well describe the non-isothermal crystallization process for the samples. The results revealed that MWNTs could accelerate the crystallization process of MCPA6, attributing to the nucleating effect of the nanofillers. Finally, the effective energy barrier for non-isothermal crystallization was evaluated as a function of the relative crystallinity by applying an isoconversional method.