A novel phosphorus-containing novolac (DOPO-PN) from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 4-hydroxyl benzoaldehyde was obtained via simple addition reactions. The chemical structure of the obtained DOPO-PN was characterized with FT-IR, 1H and 31P NMR and elemental analysis. The DOPO-PN novolac, with multi-phenol groups in the molecular chain, was used as a poly-functional curing agent for epoxies. The activity and activation energies of the DOPO-PN curing reactions with epoxies were investigated with differential scanning calorimetry (DSC). The thermal properties and thermal degradation behaviors of the DOPO-PN-cured epoxy resins were also studied with DSC and thermogravimetric analysis. High glass transition temperatures (above 160°C) and extremely high thermal stability (above 300°C) were observed for the DOPO-PN/CNE200 (o-cresol novolac epoxy)-based resins. High char yields and high limited oxygen index (LOI) values were also found to demonstrate the good flame retardancy of the DOPO-PN-cured epoxy resins. The LOI values of the epoxy resins were proportional to the phosphorus contents of the epoxy resins. A least phosphorus content of 2 wt% is detected for the DOPO-PN-cured epoxy resins to exhibit a LOI value of 26 and to pass the UL 94V-0 test. ; JNL0001548