PROBLEM TO BE SOLVED: To provide a method for producing polyphenylene oxide, which can improve the moldability at the time of molding and reduce the dielectric constant and the dielectric loss tangent of a molded cured product. SOLUTION: The molecular weight is reduced by reacting polyphenylene oxide with a monofunctional phenol. The low molecular weight polyphenylene oxide obtained by the decomposition rearrangement reaction has a low polarity and a low dielectric constant, and can be suitably used as a molding material for a low dielectric constant laminated board.