The miscibility of poly(3-hydroxybutyrate) (PHB) with ethylene-vinyl acetate (EVA) copolymers containing 70 or 85 wt% of vinyl acetate was investigated. The blend of PHB and EVA70 was found to be immiscible, because the glass transition temperature, the melting temperature and the spherulite growth rate under the isothermal crystallization conditions were independent of the blend composition. However, the melting temperature, the spherulite growth rate and the equilibrium melting temperature of the PHB/EVA85 blend decreased with an increase in the EVA85 content and the Flory-Huggins interaction parameter of the blend was negative. Therefore, PHB was found to be miscible with EVA85.