New phosphorylated epoxy polymers were obtained with a cyclic phosphine oxide epoxy, 10-phenylphenoxaphosphine-3,8-diglycidylester-10-oxide (EPCAO), cured with three types of curing agents: N,N'-(4,4'-diphenylsulfone)bis(trimellitimide) (DIDA), 10-phenylphenoxaphosphine-3,8-dicarboxylic acid-10-oxide (PACO), and phthalic anhydride (PA). In addition, compositions of the new EPCAO synthesized with these three curing agents (DIDA, PACO, and PA) were used to make a comparison of EPCAO's curing reactivities and heat and flame retardancy with those of Epon828 and DEN438. The reactivities were measured by differential scanning calorimetry. Through the evaluation of thermogravimetric analysis, those polymers that were obtained through the curing reactions between the cyclic phosphine oxide epoxy resin and the three curing agents mentioned also demonstrated excellent thermal properties and a high char yield.