Primary nucleation behavior of isotactic poly(styrene) was studied in a wide range of crystallization temperatures (T-c), times, and melt temperatures (T-f). Samples were melted at several melt temperatures (T-f) from 225 to 250 degrees C (or vice versa) and then isothermally crystallized. Time dependence on the nucleation behavior showed a sigmoidal curve with an induction time (tau(0)). The spherulites sporadically appeared (the steady state of nucleation, I) until they reached a limiting number of nuclei (the saturated nucleation density, N-s). The number of nuclei reached saturation much earlier than the induction time (tau(over)) in the overall crystallization. N-s was not associated with impingement of spherulites, since about 90% of the melt region remained. It was found that there was a critical spherulite size, in which induced nucleation sites began to appear within the outline of the original spherulite in the subsequent crystallization. When the crystallization was stopped before reaching the critical spherulite size, there was no melt temperature dependence on the nucleation behavior. On the other hand, when spherulites were grown beyond the critical spherulite size, a large number of small spherulites (granular structure) appeared within the outline of the original spherulite in the subsequent crystallization. The number of additional nucleation sites increased with an increase in the original spherulite size, and the increment of nucleation sites decreased with an increase in T-f. These granular structures could be due to insufficient melting of the crystal structure in the original spherulite, which will induce nucleation sites as a self-seeding effect upon subsequent crystallization. N-s increased by a factor of several thousand with a decrease in T-f from 250 to 225 degrees C. The crystallization temperature dependence on the nucleation rate has a bell-shaped curve with a maximum nucleation rate (I-max at T-imax). Both I-max and T-imax decreased with an increase in T-f up to about 240 degrees C and then remained constant values. I-max is a function of nucleation sites and is expressed by a power law of N-s(0.5). The nucleation density was found to be a function of the amount of 3(1)-helix composed with 5 monomeric units remaining in the melt.