Abstract: Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) was studied in this paper. poly( 3-hydroxybu tyrate)possesses a narrow melting range, a high crystallinity, large spherulite sizes and brittle fracture, which limited its application.When copolymerized with 4-hydroxybutyrate, several properties were im proved.With increasing the amount of 4HB, melt flow rate decreased from 20.7g/10 min to 8.9 g/10 min viscosity number increased 1.8 times, melting range was widened to T=150~170 ℃，and crystallinity decreasedfrom 11.57 % to 5% and spherulites were no longer observed. In addition, the tensile strength decreasedfrom 13.5to7.9MPa,elongation at break increased from 796 % to 1 020 %,glass temperature was increased from-7.29℃to-3.17℃，which is beneficial to processing.

Key words: poly ( 3一hydroxybutyrate-co-4-hydroxybutyrate) copolymer, biodegradability, property