Amorphous thin films of isotactic polystyrene (i-PS) were prepared by casting a hot solution inp-xylene onto the hot water surface. Dried films mounted on the specimen grids for transmission electron microscopy (TEM) were crystallized from the glassy state by annealing. The crystalline thin films of i-PS thus prepared were examined by TEM. In these films, we could observe immature and more or less mature two-dimensional spherulites and sheaflike structures, the constituents of which are basically edge-on lamellae. As for the space-filling mechanisms of spherulitic growth, some models have been proposed so far: for example, a model based on branching of straight lamellae and a model based on "spawning" of new lamellar crystals. In the latter model, however, most of the spawned lamellae are to be curved. From TEM observations, it is deduced that both branching and spawning occur together in the process of spherulitic growth of i-PS, because some lamellae are seemingly straight and branched but the majority of lamellae are curved. In addition, the (300) lattice images obtained by high-resolution TEM have successfully visualized, at the molecular level resolution, the two manners for producing such curved lamellar crystals with an edge-on orientation in crystalline thin films of i-PS.