Crystallization behavior of poly(3-hydroxybutyrate)(PHB) blended with poly(ethylene-co-vinylacetate) (EVA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-HV) copolymer has been studied on a polarizing microscope equipped with a hot stage. PHB equilibrium melting temperatures(Tom) calculated with the HofEnan-Weeks equation decreased a line with increase in EVA content. With the PHB/EVA blend samples, PHB spherulite radial growth rates(G) remained constant during the entire course of crystallization. It is believed to be due to the phase separation between the two components occurring prior to the crystallization. With PHB-HV copolymers, PHB-HV equilibrium melting temperatures(Tom) decreased with the increase in HV content and, at a given crystallization temperature(Tom), G was significantly reduced by the HV component. PHB was observed to crystallize in regime III at lower temperatures and in regime II at elevated temperatures. The regime II-III transition has been observed to occur at around 135$^{circ}C$. For the copolymers, similar transition behavior has not been observed for the temperature range used in the study.