Addition of the amino acids threonine, isoleucine, and valine into culture medium greatly increased the molar fraction of 3-hydroxyvalerate (3HV) in the copolyester of S-hydroxybutyrate (3HB) and 3HV produced by Alcaligenes sp. SH-69. In shake flask cultures, addition of threonine, isoleucine, or valine into culture medium resulted in 53.0, 40.7, or 14.8 mol% 3HV in the copolyester, respectively. The 3HV content in the copolyester was 14 mol% and 27 mol% in Jar fermenter cultures containing 10 mM and 20 mM threonine, respectively. Similar molar fractions of 3HV (11-14 mol%) in the copolyester were obtained in experiments carried out with culture media containing 10 mM isoleucine or valine. The 3HV content in the copolyester increased as amino acid concentration increased. Addition of the amino acids into culture medium at different culture times revealed that final 3HV contents were similar irrespective of addition time except for the case when glucose was depleted.