The spherulitic and lamellar morphologies of isotactic polystyrene (iPS) isothermally crystallized from the glassy state were investigated by polarized light microscopy (PLM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The AFM phase images and TEM bright-field electron micrographs revealed that the iPS spherulites consist of a number of dominant edge-on lamellae which continuously grow outward by splaying and branching. By partial melting, the less perfect subsidiary lamellae, which are formed within the framework of the dominant ones due to the growth in restricted spaces and possess lower thermal stability than that of the dominant ones, were directly observed by TEM.