The melting and crystallization behaviour and phase morphology of poly(3-hydroxybutyrate) (PHB) and hydroxyethyl cellulose acetate (HECA) blends prepared by casting films have been studied by differential scanning calorimetry (d.s.c.), Fourier transform infra-red (FTi.r.), scanning electron microscopy and polarizing optical microscopy. The melting temperatures of PHB in the blends were independent of the blend composition with PHB contents above 20%. The melting enthalpy of the blends decreased with increase in the HECA component and was close to the additive value of the enthalpy of the two components. The glass transition temperatures of PHB in the blend were constant at about 8 degrees C. No specific interaction between the two components was found by FTi.r. The crystallization of PHB in the blend was affected by the HECA component, especially in the PHB/HECA (20/80) blend. During the d.s.c. cooling run at a lower cooling rate, two separate transitions were found for PHB/HECA (80/20), (60/40) and (40/60) blends, which corresponded to the crystallization of PHB and the phase transition of HECA from an isotropic phase to a mesophase in the blends, respectively. The phase transformation of HECA from an isotropic phase to a mesophase was almost independent of the PHB component.