A modified polyphenylene ether resin is provided which is a product of the reaction of 100 parts by weight of (A) a polyphenylene ether having a main chain structure of the following formula (1): (wherein R1 and R4 each independently represents hydrogen, a primary or secondary lower alkyl, a phenyl, an aminoalkyl or a hydrocarbonoxy, and R2 and R3 each independently represents hydrogen, a primary or secondary lower alkyl or a phenyl), with 0.01 to 10.0 parts by weight of (B) a modifier selected from conjugated non-aromatic diene compounds, dienophilic compounds having one dienophile group and precursors of the diene or dienophilic compounds, wherein the number of rearrangement structures each represented by the following formula (2): (wherein R1, R2, R3, and R4 have the same meanings as defined above in the formula (1)) is less than 0.01 per 100 phenylene ether units of the formula (1).