A novel polyhydroxyalkanoate (PHA) synthase derived from a microorganism capable of producing a PHA having a novel side-chain structure and a DNA encoding the amino acid sequence for the synthase are provided. Two PHA synthase proteins (SEQ ID NOs: 1 and 3) derived from Pseudomonas cichorii YN2 (FERM BP-7375) and PHA synthase genes encoding these PHA synthases are provided, respectively (SEQ ID NOs: 2 and 4). A recombinant microorganism is endowed with a PHA producing ability.