The structure development and crystallization behavior of poly(propylene) (PP) filled with wollastonite mineral was studied with respect to different particle sizes of the filler. The decrease in particle size led to increase in crystallization rates and decrease of crystallization half time, indicating greater nucleation efficiency for smaller sizes of the wollastonite particles. This was also reflected in the higher crystallinity values obtained for small filler particles. The WAXD analysis of PP/wollastonite revealed significant changes in the relative intensity of certain peaks (110 reflection) at small particle size, indicating preferential growth of PP on wollastonite. The exact co-relationship of nucleation rate/crystallization rate and the additive particle size (d) was determined which showed that for any given concentration of the additive, it was proportional to (1/d)3.