Two cloned phbC genes, encoding polyhydroxybutyrate (PHB) synthase from Ralstonia eutropha and from Alcaligenes latus, were transformed into a PHB-negative mutant of R. eutropha. The expression characteristics of both genes were compared for the biosyntheses of PHB and its copolymers. Each phbC gene had different characteristics not only in the biosyntheses of PHB, poly(3-hydroxybutyrate-3-hydroxy-valerate), and poly(3-hydroxybutyrate-4-hydroxybutyrate) but also in the resulting morphology of PHB granules.