We report on the optical planar waveguides formation and modal characterization in beta-BaB2O4 crystals by Ni2+ ion implantation at energy of 3.0 MeV and doses of similar to 10(14) ions/cm(2). The prism coupling method was used to investigate the dark-mode property at wavelengths of 633 nm and 1539 nm, respectively. The refractive index profiles of the waveguides with different doses were reconstructed by an effective refractive index method based on the reflectivity calculation method (RCM). The modal analysis indicates that the fields of TM modes can be well restricted in the guiding region, which means the formation of non-leaky waveguide in the crystal. (C) 2008 Elsevier B.V. All rights reserved.