Effects of IPN (Interpenetrating Polymer Network) structures on the nonlinear optical properties of the polymers were studied. The IPN's were prepared using simultaneous polymerization, spin coating and post curing. The second order nonlinear optical properties of polymer films were evaluated by Maker-fringe experiment using the facilities in IBM research center at Almaden. The noncentrosymmetric structure for second order optical nonlinearity was obtained by applying an electric field using corona poling. The d33 values of epoxy,semi-IPN(50/50) and acrylic resin were 12.2 pm/V, 4.2 pm/V and 0.9 pm/V respectively. Semi-IPN had good stability after initial decay.