The effects of tacticity and molecular weight (MW) of isotactic polypropylene (iPP) on crystallization kinetic and crystal morphology were investigated by in-situ isothermal crystallization using simultaneous synchrotron small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM) techniques. Several quantitative parameters were extracted and analyzed in details. It was found that tacticity notably influenced the rate of nuclei seeding, where the high-tacticity iPP sample exhibited a faster nucleation rate. However, tacticity affected only slightly on the crystallization and normalized spherulite-growth rates. Inversely, the MW strongly influenced the crystal lamellar morphology, in which the amorphous layer thickness (L-a) was found to be larger in high-MW iPP than that in low-MW iPP. These findings indicated the behavior of "tapering" in the lamellar width during crystal growth, where tacticity and MW both played a role in this process.