The biodegradation behavior of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) film in the presence of pseudomonas mendocina was studied. The biodegradation shows two steps degradation mechanism with first slowly and then faster. The degradation rate is nearly 95%after degradation 10 d. The surface of the degraded films at different degradation stages is observed by scanning electron microscopy. It is observed that the surface of the films is eroded and covered with holes,and the erosion and the size of holes increase with the extension of degradation time. The results of differential scanning calorimeter reveal the melting temperature of the degraded films increases and the relative crystallinity decreases with the extension of degradation time respectively. The results of X-ray diffraction further evidence the decrease of the crystallinity. The results of thermo gravimetric analyzer indicate that the thermal stability of the degrade films decreases after degradation.%以门多萨假单胞菌为降解菌株，研究了聚3–羟基丁酸与4–羟基丁酸共聚物[poly(3HB-co-4HB)]薄膜的微生物降降过程。门多萨假单胞菌对poly(3HB-co-4HB)薄膜的降解可分为慢速降解阶段和快速降解阶段。经10 d的降解，薄膜的降解率可达到94.7%。扫描电子显微镜观察发现，经微生物降解的薄膜表面因降解而形成的孔洞及蚀痕，这些孔洞及蚀痕随着降解时间的增加有着加大和加深的情况。差示扫描量热法分析发现，随微生物降解时间的增加，薄膜的熔点上升，而相对结晶度降低。X射线衍射分析结果也进一步证实了薄膜经微生物降解后相对结晶度的降低。热重分析法也证明薄膜的热稳定性随降解时间增加而下降。
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