Melt nucleation and crystallization behavior of homo-isotatic polypropylene (homo-iPP), maleic anhydride (MAH)-grafted-iPP, and MAH-modified IPP, produced from iPP and a small amount of MAH-grafted-iPP, was investigated by polarizing optical microscopy (POM), at T-c = 121-135 degrees C. Nucleation processes at a given T-c were faster for modified PP as compared to neat iPP. The induction time for nucleation increased nonlinearly with increasing T-c and decreased for modified PP, probably as a result of promoted heterogeneous nucleation due to the presence of carbonyl groups of MAH-grafted-PP. The average spherulite sizes were decreased by modification, and the growth rate was enhanced in maleated PP and modified PP. The induction time approach was applied to the results obtained by POM to compare the tendency for heterogeneous nucleation of neat and MAH-modified PP.