The miscibility behaviour of biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvale) (PHB-HV) blended with poly(vinyl chloride) (PVC) was investigated by using differential scanning calorimetry, dynamic mechanical thermal analysis, Fourier-transform infra-red spectroscopy and a mechanical testing system. A blend of PHB-HV containing 8% HV (PHB-8HV) with PVC was immiscible, showing two separate T-g values in all compositions; whereas a blend of PHB-HV containing 18% HV (PHB-18HV) with PVC was miscible, showing a melting-point depression and a single T-g in the whole range of compositions. For the PHB-18HV/PVC system, the C-O-C stretching vibration at 1183 cm(-1) of PHB-18HV and the CH-Cl deformation at 1254cm(-1) of PVC were shifted, indicating that there exists a specific intermolecular interaction between the two components. In addition, as the PVC component was increased, tensile strength and Young’s modulus were increased, while the inverse behaviour was observed in elongation at break.