A method of recovering polyhydroxyalkanoates (PHAs) from municipal waste sludge includes: (a) removing coarse particles in the municipal waste sludge and measuring a solid content in the municipal waste sludge in terms of a volatile suspended solid in the municipal waste sludge; (b) removing a supernatant from the municipal waste sludge; (c) freezing the municipal waste sludge; (d) adding a controlled amount of sodium hypochlorite solution to the municipal waste sludge that has been frozen, a ratio of the solid content of the municipal waste sludge to a volume of the sodium hypochlorite solution added in step (d) ranging from 0.67 mg/ml to 4 mg/ml and being defined as a liquid-solid ratio; and (e) separating PHAs from non-PHAs substances in the municipal waste sludge obtained in the step (d).