The growth behaviors of cross-hatched and lath-like lamellae of α-form spherulites and flat-on lamellae of β-form pherulites of isotactic polypropylene were studied with a high-temperature atomic force microscopy in situ and in real time. The growth rates of crystal lamellae in types I, II and mixed α-form spherulites and in β-form spherulites, as well as the spatial frequency of tangential branching, were measured. The frequency of tangential branching increases with decreasing crystallization temperature, while the growth rates of leading radial and tangential lamellae are approximately the sane at a given temperature. Observations of as-crystallized materials demonstrated that the spacing and length of transverse lamellae is sufficient to differentiate among spherulite types. Height measurements in the melt near the growth surface indicate roles of molecular transport in the crystallization process. © 2005 Elsevier Ltd. All rights reserved.