Photovoltaic response and optical spectra of lithium niobate crystals (LN) grown from K 2 O-containing melt and/or doped with Mg and Fe have been studied. It has been found that growing of LN crystals at the presence of K 2 O-flux, Mg-doping and increasing of Li/Nb ratio have influence on the physical properties of the crystals, which evidences approaching of the composition of these crystals to the stoichiometric one.