Inorganic nanotubes (INT) were used for the first time to prepare advanced polymer nanocomposites by means of the most simple, cost-effective and ecologically friendly way (i.e., melt-processing route). The polymer matrix was isotactic polypropylene (iPP) and the inorganic fillers were molybdenum disulfide nanotubes (MoS2). The effect of INT-MoS2 concentration and the crystallization temperature on the isothermal crystallization behavior of iPP was investigated using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXS). It has been observed that INT-MoS2 affects the crystallization of nanocomposites remarkably, which can be attributed to the nucleating effect of INT-MoS2 on the monoclinic alpha-crystal form of iPP. Other parameters such as the Avrami exponent and the fold surface free energy of crystallization of iPP chains in the nanocomposites were obtained in order to determine the effect of the INT-MoS2 on them. The addition of INT-MoS2 remarkably influences the kinetics of nucleation and growth of iPP with a decrease in the fold surface free energy of 11-24%.