The polyaddition of bisphenol A diglycidyl ether (BPGE) with bis(4-chlorophenyl) phenylphosphonate was carried out using quaternary onium salts or crown ether complexes as catalysts. When the polyaddition was performed using tetrabutylammonium chloride, tetrabutylphosphonium chloride, or 18-crown-6/KCl in N-methyl-2-pyrrolidone at 110 degrees C for 48 h, the corresponding polyphosphonate with moderated molecular weights was obtained in 88-96% yields. The structure of the resulting polyphosphonate was confirmed by IR and H-1-NMR spectra. The polyaddition of BPGE with various diaryl phosphonates also proceeded very smoothly to produce the corresponding polyphosphonates with moderate molecular weights.