To study the effect of arene substitution patterns of phenylenediamines, as curing agents, on curing behaviors, thermal and mechanical properties of epoxy resins, DGEBF(Diglycidyl ether of bisphenol F) and o, m, p-phenylenediamine(PDA) were selected. The cure kinetics of epoxy mixtures were analyzed under both dynamic and isothermal conditions using differential scanning calorimetry(DSC). The activation energy and curing initiation temperature were found to be lowest with p-PDA and highest with o-PDA and it resulted that the degree of cure and curing rate were highest and fastest with p-PDA and lowest with o-PDA. Tg and thermal stability of the epoxy samples were better with o-PDA and m-PDA than p-PDA. Tensile strength and fracture toughness were highest with m-PDA and lowest with p-PDA. These results indicated that m-PDA could be the best curing agent of isomeric PDAs. And mechanical properties of the epoxy resin could be different only by the isomeric structures of curing agents.