Abstract: The changes of thermal and tensile properties of the pure poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and PHBV containing boron nitride (BN) with aging time at 30℃ (above T_g) were studied.The mobile amorphous fraction (X_MA),rigid amorphous fraction (X_RA) and crystalline fraction (X_c) of PHBV were determined by modulated differential scanning calorimetry (MDSC) according to the polymer three-phase model. Results showed that addition of nucleating agent approach represented an efficient strategy to suppress the physical aging process of PHBV which was further confirmed by the dynamic mechanical and tensile properties data, as well as the crystal morphology.