The phase behaviour, crystallization kinetics and tensile properties of poly(P-hydroxybutyrate)-cellulose propionate (PHB-CP) blends have been investigated using differential scanning calorimetry, optical microscopy and tensile testing measurements. The results show that the blends are miscible as evidenced by the observation of a single composition-dependent glass transition temperature, a depression of the equilibrium melting temperature of PHB, and a decrease in the spherulitic growth rate of the PHB component. Finally, in the study of the tensile properties it is shown that an improvement in the ductility of PHB is brought about by blending with CP.