Monomode KTiOPO4 waveguide was formed by ion implantation with 500 keV O+ ions at a dose of 1×1015 ions cm-2 and the following ion exchange in pure RbNO3 at 340 °C for 45 min. Results indicate that it is an effective method to modulate the waveguide modes by combining ion exchange with ion implantation. Positive changes in both nx and ny refractive indices occur in the waveguide region. Continuous and homogenous field pattern of the propagation light in the waveguide was collected and studied using the end-coupling method. The irradiation damage as well as the Rb distribution was analyzed by means of the Rutherford backscattering spectrometry technique. The concentration profiles of Rb and K in KTiOPO4 were measured by the time of flight secondary ion mass spectrometry. Results show that the lattice damages formed by ion implantation act as a diffusion barrier, which stop the Rb ion and K ion exchange in the deeper depth.