The cure kinetics of off-stoichiometric biphenyl epoxy (4,4-diglycidyloxy-3,3',5,5'-tetramethyl biphenyl)-dicyclopentadiene type phenolic resin system by differential scanning calorimetry(DSC) using an isothermal approach were investigated. The epoxy/hydroxyl (E/H) ratios of stoichiometric (E/H = 1), excess phenol off-stoichiometric (E/H = 0.8) and excess epoxy off-stoichiometric (E/H = 1.2) of epoxy and phenolic group were selected and all kinetic parameters of the cure reaction including the reaction order, activation energy and the rate constant were calculated and reported. To describe the curing reaction after the vitrification controlled by diffusion factor, the semiempirical relationship proposed by Chern and Poehlein and the calculated parameters were used. A one-to-one relationships, which is independent of the cure temperature, between the glass transition temperature and the fractional conversion were interpreted using DiBenedetto equation. Time-Temperature-Transformation (TTT) isothermal cure diagram has been established at each equivalent weight ratio using the kinetic model coupled with diffusion factor and the DiBenedetto equation.