The possibility of using poly(1,3-phenylene methylphosphonate) (PMP) pre-reacted with low molecular weight bisphenol A epoxy resin for the preparation of flame retardant epoxy resins has been investigated. The molar ratio of the reactants was adjusted to obtain a phosphorus content in the end product of 2.00 or 2,17 %. Triphenylphosphine, 2-methyl imidazole, triethanolamine and tetrabutylphosphonium bromide were used as catalysts. The effects of type and concentration of catalyst on the reaction course were investigated. The synthesis was carried out in the melt and the reaction progress was followed by determination of the epoxy values of the samples taken during the reaction. The viscosity of the samples and their molecular weight distribution were determined as well. The influence of an ionic chlorine present in the epoxy resin on the course of the reaction was investigated. For selected samples 31P NMR spectra were recorded. The reaction conditions were chosen in such a way to avoid a gelation during the process. The application of the resins prepared in this way in the flame retardant epoxy systems will be reported soon.