Pseudomonas sp. 61-3 accumulated a blend of poly(3-hydroxybutyrate) [P(3HB)] homopolymer and a random copolymer consisting of 3-hydroxyalkanoate (3HA) units of 4-12 carbon atoms. The genes encoding beta-ketothiolase (PhbAR(Re)) and NADPH-dependent acetoacetyl-CoA reductase (PhbB(Re)) from Ralstonia eutropha were expressed under the control of promoters for Pseudomonas sp. 61-3 pha locus or ii. eutropha phb operon together with phaCl(Ps) gene (PHA synthase 1 gene) from Pseudomonas sp. 61-3 in PHA-negative mutants P. putida GPp104 and R. eutropha PHB(-)4 to produce copolyesters [P(3HB-co-3HA)] consisting of 3HB and medium-chain-length 3HA units of 6-12 carbon atoms. The introduction of the three genes into GPp104 strain conferred the ability to synthesize P(3HB-co-3HA) with relatively high 3HB compositions (up to 49 mol%) from gluconate and alkanoates, although 3HB units were not incorporated at all or at a very low fraction (3 mol%) into copolyesters by the strain carrying phaCl(Ps) gene only. In addition, recombinant strains of R. eutropha PHB(-)4 produced P(3HB-co-3HA) with higher 3HB fractions from alkanoates and plant oils than those from recombinant GPp104 strains. One of the recombinant strains, R. eutropha PHB(-)4/ pJKSc46-pha, in which all the genes introduced were expressed under the control of the native promoter for Pseudomonas sp. 61-3 pha locus, accumulated P(3HB-co-3HA) copolyester with a very high 3HB fraction (85 mol%) from palm oil. The nuclear magnetic resonance analyses showed that the copolyesters obtained here were random copolymers of 3HB and 3HA units.