To provide a novel polyhydroxyalkanoate having a reactive functional group in a molecule and a method of producing the same; and a novel polyhydroxyalkanoate having a new function obtained by chemically modifying the polyhydroxyalkanoate having a reactive functional group and a method of producing the same. By utilizing a vinyl group of a polyhydroxyalkanoate containing a unit having the vinyl group at a side chain thereof, a polyhydroxyalkanoate containing units having a carboxyl group, an amide group, and a sulfonic group in a molecule is induced.