A novel amine-terminated and organophosphorus-containing compound m-aminophenylene phenyl phosphine oxide oligomer (APPPOO) was synthesized and used as curing and flame-retarding agent for epoxy resins. Its chemical structure was characterized by Fourier transform infrared (FTIR) spectroscopy, 1H nuclear magnetic resonance (1H NMR), 13C nuclear magnetic resonance, and 31P nuclear magnetic resonance. The flame-retardant properties, combusting performances, and thermal degradation behaviors of the cured epoxy resins were investigated by limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimeter test, and thermogravimetric analysis. The EPO/APPPOO thermosets passed V-1 rating with the thickness of 3.0 mm and the LOI value reached 34.8%. The thermosets could pass V-2 rating when the thickness of the samples was 1.6 mm. The cone calorimeter test demonstrated that the parameters of EPO/APPPOO thermosets including heat release rate and total heat release significantly decreased compared with EPO/PDA thermosets. Scanning electron microscopy revealed that the incorporation of APPPOO into epoxy resins obviously accelerated the formation of the compact and stronger char layer to improve flame-retardant properties of the cured epoxy resins during combustion. The mechanical properties and water resistance of the cured epoxy resins were also measured. After the water-resistance test, EPO/APPPOO thermosets still remained excellent flame retardant and the water uptake was only 0.4%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41159.