The invention provides a PHA copolymer including at least a 3-hydroxy-.omega.-carboxyalkanoic acid represented by a formula (19) or (32) and simultaneously at least a unit represented by a formula (2) or a formula (3) in a molecule, a precursor PHA copolymer having a corresponding vinyl group or a corresponding alkoxycarbonyl group, a biosynthesis method thereof by microorganisms, and a method of producing a desired PHA copolymer from the precursor PHA copolymer: (wherein k, m, n are integers; R.sub.18 represents H, Na, K, R27? represents (A); R.sub.1 represents a substituent on a cyclohexyl group and represents H, CN, NO.sub.2, a halogen atom, CH.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7, CF.sub.3, C.sub.2F.sub.5, or C.sub.3F.sub.7; R includes a residue including a phenyl structure or a thienyl structure; these being independent for each unit). ##STR00001##