Two initially heavily entangled multiwall carbon nanotube (MWCNT) systems are well dispersed in polypropylene (PP) by a two-step process of solid-state shear pulverization (SSSP.) followed by melt mixing (MM), and the dispersion and property enhancements are studied as a function of the specific energy input during SSSP. Pulverization of 99/1 wt% PP/MWCNT hybrids with MWCNT diameters of 30-50 nm results very small, loose agglomerates interpenetrated by PP; subsequent MM results in individual tubes dispersed in PP even at relatively low SSSP energy input. When much thinner and more heavily initially entangled MWCNTs with diameters less than 8 nm are used, MWCNT bundles with size up to 500 nm remain even at the highest SSSP energy input. For both systems processed by SSSP followed by MM, the Young's modulus, degradation temperature, and crystallization rates are increased dramatically with increasing SSSP energy input, in accord with better MWCNT dispersion.