Thermoanalytical and crystal growth investigations of the ternary system Cs2O–Li2O–Nb2O5 are presented in order to grow stoichiometric LiNbO3 (LN) crystals. Part of the phase diagram is determined and subsolidus phases are identified at room temperature by X-ray powder diffraction. Among the constituent phases, a new tetragonal cesium lithium niobate phase is assessed. From the Cs2O–Li2O–Nb2O5 system, good quality quasi-stoichiometric LN crystals can be grown.