Laser spectroscopy has been applied to systematically investigate the effect of MgO or ZnO codoping on the Nd3+ centres formed in LiNbO3. Both codopant oxides produce the same effect, so two new Nd3+ centres appear in both LiNbO3(MgO):Nd and LiNbO 3(ZnO):Nd crystals. These new centres correspond to a small percentage (less than 1%) of Nd3+ ions, which are displaced from Li+ sites to a new lattice site. The possible sites for these Nd 3+ centres are discussed.