The flame retardancy and the rearrangement reaction of polyphenylene-ether [poly-(oxy-2,6-dimethyl-1,4-phenylene), PPE] and polyphenylene-ether/polystyrene (PS) alloys have been studied. The flame retardancy of PPE blended with phosphates was proportional to PPE content as well as to the phosphates. The surface temperatures of PPE during a combustion was higher than that of PS, whereas PPE is more flammable than PS. The element analysis of the polymer surface showed that carbon was richer compared with the content of the newly synthesized PPE. Four monomeric and eight dimeric scission products were recovered by thermogravimetric-mass (TGA-MASS) analysis at high temperature in inert atmosphere. These structures of the scission products suggested that the rearrangement reaction occurred in combustion at high temperature. Namely, the formation of carbonaceous materials on the surface followed the rearrangement reaction and dehydration which was accelerated by the addition of aromatic phosphates.