Poly(vinylidene fluoride) (PVDF) nanocomposites containing homogeneously dispersed multi-walled carbon nanotubes (MWCNTs) and carbon black (CB) were fabricated by a small melt mixer. The uniform dispersion of the nanofillers in PVDF was confirmed by both scanning electron microscopy and transmission electron microscopy. Both the heterogeneous nucleation efficiency and crystallization half-time show that MWCNTs exhibit higher nucleation efficiency than CB for the crystallization of PVDF. Meanwhile, MWCNTs show greater contribution to the reinforcement of the storage modulus of PVDF as revealed by dynamic mechanical analysis, especially at low temperatures. However, the enhancement of the storage modulus in the melt state is reversed due to the network formed by serious agglomeration of CB. This study provides some insights into the nucleating and reinforcing efficiency of MWCNTs and CB in polymers.