A planar optical waveguide has been formed in a LiB 3 O 5 crystal using 6.0MeV Cu + -ions with a dose of 1×10 15 ions/cm 2 at room temperature. Possible propagating modes were measured at a wavelength of 633nm using the prism-coupling method. The refractive index profiles of the waveguide were reconstructed by an effective refractive index method and the beam propagation method was used to investigate the properties of the propagation modes in the formed waveguide. The results suggest that the fundamental TE 0 and TM 0 modes may be well-confined and propagate a longer distance inside the waveguide. The implantation process was also simulated using the transport of ions in matter code (TRIM), which indicates that the nuclear energy deposition may be the main factor for the refractive index change.