A novel phosphorous-containing biphenol, 2-(5,5-dirnethyl-4-phenyl-2-oxy-1,3,2-dioxaphosphorin-6-yl)-1,4-benzenediol (DPODB), was prepared by the addition reaction between 5,5-dimethyl-4-phenyl-2-oxy-1,3,2-dioxaphosphorinane phosphonate (DPODP) and p-benzoquinone (BQ). The compound (DPODB) was used as a reactive flame retardant in o-cresol formaldehyde novolac epoxy resin (CNE) for electronic application. The structure of DPODB was confirmed by FTIR and NMR spectra. Thermal properties of cured epoxy resin were studied using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The flame retardancy of cured epoxy resins was tested by UL-94 vertical test and achieved UL-94 vertical tests of V-0 grade (nonflammable) (c) 2006 Wiley Periodicals, Inc.