Undoped and MgO-doped LiNbO3 single crystals with near-stoichiometric compositions were grown from K2O-doped melts and Li-rich melts by two different growth techniques. Near-stoichiometric LiNbO3 single crystals. having large [Li]/[Nb] ratios of 0.988-0.993. showed smaller threshold concentrations of MgO than congruent crystals for the behavior of Curie temperature. OH absorption band and optical damage properties. We discuss the ideal defect structure models, and find that the Li-site vacancy model is consistent with the experimental results for MgO-doped near-stoichiometric LiNbO3 single crystals.