Novel phenolic novolac resins, bearing phthalonitrile groups anchored to benzene ring through phenyl azo linkage were realized by the coupling reaction between novolac and phthalonitrile diazonium salt. The diazo-coupling occurred to a maximun of about 61%. The apparent molecular weight, determined form GPC showed a downward drift with increase in degree of phthalonitrile substitution. Analysis using DSC technique indicated that the resin underwent curing in a temperature range form 290 to 320 degrees C. The curing occurred via addition polymerization of phthalonitrile groups. The thermal stability and anaerobic char yield of the polymers increased proportion to the crosslinking. The probable cure mechanics were discussed.