Polypropylene (PP) was lightly maleated by solid-state graft polymerization and further neutralized to prepare semicrystalline ionomers, H+-, Na+-, Ca2+- and Mn2+-form maleated PP (mPP). The crystallization kinetics of pure PP and these ionomers have been investigated under isothermal and non-isothermal conditions. Under both conditions, the introduction of pendant groups along the PP chains increases the crystallization rate and does not influence the crystallization mode. The energy required for folding macromolecules to form nuclei becomes smaller in case of ionomers. The facility of nucleation in ionomers by the ionic interactions may result in high crystallization rate, while the decrease of chain diffusion in mPP ionomers has a reverse effect at the same time.