Blends of P(3-hydroxylbutyrate-co-4-hydroxylbutyrate)［P(3HB-co-4HB)］plasticized by triethyl citrate (TEC), soybean oil (SO) and glycerin triacetate (TA) have been prepared by a solvent casting film method. The effects of varying the type and content of plasticizer on the properties of the polymer blends have been studied. The crystalline behavior and mechanical properties of the blends were investigated by differential scanning calorimetry (DSC) and tensile measurements. The results showed that the effect of TEC on the crystalline temperature (T_mc) and crystalline enthalpy (ΔH_mc) is the smallest of the three plasticizers. For a mass ratio of TEC of 5%, T_mc decreased by 2℃ and ΔH_mc remained almost unchanged as compared with the pure polymer. Furthermore, adding TEC had a significant effect on the glass transition temperature (T_g) of the blend and for a mass ratio of TEC of 20%, T_g decreased by 21℃. In the case of a mass ratio of TEC of 5%, the TEC/polymer blend had a tensile strength of about 15.8MPa and an elongation at break of about 588%, comparable to the values for the pure polymer.