The first MeV phosphor ion implanted planar optical waveguide in KTiOPO4 (KTP) is reported. The modes in the KTP waveguide were measured by dark mode coupling method using a model 2010 prism coupler. The refractive index profile was analyzed by reflectivity calculation method (RCM) at room temperature, after treatment at 200 degreesC for 30 min (in air) and 77 K for 150 min (in liquid nitrogen), respectively.