An organophosphorus epoxy resin with diglycidyl ether of bisphenol A (DGEBA), which has improved fire performance, was synthesized from the reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and DGEBA. The epoxy resin was then cured with an isomeric mixture of 3,5-diethyltoluene-2,4-diamine and 3,5-diethyltoluene-2,6-diamine. The reaction kinetics were measured by Fourier transform IR, H-1-NMR, and differential scanning calorimetry. The effect of the incorporation of a phosphorus species into the epoxy network structures was also measured using thermogravimetric, thermal conductivity, and dynamic mechanical thermal analyses. The fire performance was measured using cone calorimetry, which showed that a significant improvement was achieved by the addition of only 1-4% phosphorus into the epoxy backbone. (C) 2003 Wiley Periodicals, Inc.