New symmetrical pi‐conjugated molecules having large third‐order nonlinear susceptibilities, &khgr;(3), are reported. The &khgr;(3)spectra of these molecules have been measured by a THG Maker‐fringe method. The magnitudes of the three‐photon resonant &khgr;(3)reach 10−10esu. The positions of the three‐photon resonance lie at the lowest‐energy peaks in the vibrational structure of each absorption spectra for these molecules.