A series of poly(3-hydroxybutyrate-co-4-hydroxybutyrate)s[P(3HB-co-4HB)s] sheets with the 4HB contents from about 9 to 34 mol % were prepared via melt molding. Their crystallinity, crystalline structures, thermal and mechanical properties were characterized by differential scanning calorimetry, X-ray diffraction, thermogravimetric analysis, dynamic mechanical analysis, and tensile test. It was found that the melt temperatures (T-m), glass transition temperatures (T-g) and storage modulus (E') of all the [P(3HB-co-4HB)s] copolymers investigated decreased continuously with increasing the amount of the 4HB; the-yield stress and breaking stress nearly decreased with the increase of the 4HB contents while the elongation at the yield and break points increased; and the thermal stability of the P(3HB-co-4HB)s improved with increasing 4HB contents. The results suggest that the mechanical properties and crystal lattice parameters of the melt molded sheets are somewhat different from those of the solution cast films. (C) 2008 Wiley Periodicals, Inc.