Simultaneous improvement of stiffness and toughness of isotactic polypropylene (iPP) has caught tremendous effort for decades and previously we have shown that the modification of iPP with combined nanofillers and β-nucleating agent (β-NA) is an efficacious way to balance its stiffness and toughness. However, simultaneous introduction of reinforcing fillers and β-NA generates nucleation competition in the crystallization process and generally the formation of β crystals is depressed. Once β-NA was grafted onto the surface of nanofillers, it may induce different crystallization behaviors. The spacial distribution of β-NA and nanofillers may be a very important factor to affect the crystallization behaviors of iPP matrix. In this work, a kind of novel β-NA for iPP, N,N’-dicyclohexyl-1,5-diamino-2,6-naphthalenedicarboxamide, was supported onto the surface of multi-walled carbon nanotubes (MWCNTs) through chemical bonds. Two different mixing method, solution-mixing and melt-blending, were used to prepare the iPP composites with MWCNT-NA, and the crystallization behaviors of the samples were studied. The content of β crystals in the two samples showed a huge difference. Melt-blending sample was full of β crystals while the content of β crystals in solution-mixing sample was relatively low, which is related with the spacial distribution of β-NA and MWCNTs during the mixing processes.