Blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with 12 mol% hydroxyvalerate (HV) content and epoxidized natural rubber (ENR) with 50 mol% epoxidation level were studied along with the thermal properties and morphologies. Glass transition temperatures reveal immiscibility of the polymers over the entire composition range. The equilibrium melting point (T (m) (0) ) of PHBV in blends was determined applying Hoffman-Weeks step-wise annealing procedure. There is no significant variation of T (m) (0) for PHBV with blend composition. Also the crystallinity of PHBV stays approximately constant in the blends, only a slight decrease might be recognized with increasing ENR content. The rate of crystallization of PHBV decreases with PHBV content according to a power law. Morphological studies by polarizing optical microscopy reveal a fine intraspherulitic dispersion of ENR in volume-filling PHBV spherulites, which develop during isothermal crystallization.