Abstract: It is an object of an embodiment of the present invention to provide an industrially easily applicable technology for reducing a viscosity of a culture solution, in order to collect a polyhydroxyalkanoate from a polyhydroxyalkanoate-producing microorganism. The object is attained by providing a method for producing a polyhydroxyalkanoate, including the following steps (a) and (b): (a) maintaining a culture solution at 40° C. to 80° C., the culture solution including microbial cells containing the polyhydroxyalkanoate; and (b) adding an oxidizer to the culture solution obtained in the step (a), adjusting a pH of the culture solution to 10.5 to 13.0, and maintaining the culture solution at 30° C. to 75° C.