The miscibility, crystallization and melting behaviour, and phase morphology of poly(3-hydroxybutyrate) (PHB) and ethyl cellulose (EC) blends prepared by casting films have been studied by d.s.c., FTi.r., SEM and polarizing optical microscopy. The casting films of PHB/EC (60/40), (40/60) and (20/80) blends and annealed samples of the casting films of PHB/EC (86/20), (60/40), (40/60) and (20/80) blends showed composition-dependent glass transitions, the temperature position increased with the decrease of PHB content in the blends, and reached the maximum value for the EC component. After melt quenched or d.s.c. cooling run, only a lower glass transition temperature (T-g) corresponded to that of PHB phase in the blends was found in d.s.c. trace for each blends. The T-g remained almost unchanged at about 5 or 9 degrees C. The hydrogen bonding of hydroxyl groups of EC was proved stronger than that of the hydroxyl group in EC with carbonyl group in PHB. The absorption bands of hydroxyl groups in EC decreased with the increase of PHB content in the blends, while the absorption bands of carbonyl groups in PHB were independent of the blend composition at 1723-1724 cm(-1). Unlike the PHB component, the blends displayed no crystallization when cooled from the melt during the d.s.c. non-isothermal crystallization runs. The cold crystallization peaks of the blends were presented in the following d.s.c. heating runs. The growth of PHB spherulites was delayed by EC content. Both the temperature and the heat of the cold crystallization (T-cc and Delta H-cc) were dependent on the blend composition. Higher T-cc and Delta H-cc of PHB/EC (80/20) blend than those of PHB component and other blends were found due to the stronger interaction between two components at this ratio. The T-m and crystallinity (C-r) of PHB in the PHB/EC (80/20) blend are higher than those of pure PHB in most cases because of the higher T-cc. No evidence of phase separation of the blends was observed by SEM studies.