Dielectric and electro-optical studies of a pure and electron beam irradiated liquid crystalline compound 4-(trans-40-n-hexy lcyclohexyl) iso thiocyanatobenzoate have been carried out. Dielectric anisotropy, relaxation frequency, activation energy and distribution parameter of an observed non- collective mode corresponding to the molecular rotation about the short axe shave been determined as a function of temperature and irradiation dose where as threshold and switching voltages, splay elastic constant are determined as a function of irradiation dose. The relaxation frequencies initially decrease up to an irradiation dose of 40kGy but there after increase due to irradiation. The activation energies are increased upto irradiation dose of 40kGy but around 60kGy dose of irradiation, we found decrease in the activation energy. Electro-optical measurements show the lowering of the threshold voltage with sufficient improvement in the steepness of the transmission voltage curves due to irradiation. The observed changes in the dielectric and electro-optical properties are related with the cis–trans isomerization due to electron beam irradiation.