Congruent LiNbO3 (CLN) crystals with various orientations (X-, Y- and Z-cut) and thickness (1-3.2 mm) were treated by the vapor transport equilibration (VTE) method in lithium-rich environment at 1100degreesC. Homogeneous and crack-free crystals with nearly stoichiometric composition ( > 49.9 mol% Li2O) were obtained for different orientations. The cracking problem of X- and Y-cut samples was studied and solved by decreasing the cooling rate after the VTE treatment. The Li2O content in the crystal was determined by the cutoff UV absorption edge of the crystal sample. For thick samples, the diffusion of lithium atoms from side faces had influenced the composition homogeneity of the VTE-treated crystals. The CLN crystal plates with thicknesses of around 2 turn were converted into stoichiometric LiNbO3 (SLN) by the VTE method within 200 h. Thicker CLN samples would need longer time to be converted into SLN. (C) 2003 Elsevier B.V. All rights reserved.