We report a method for fabricating Rb/Ba ion exchanged optical waveguides in Z cut KTiOPO 4 (KTP). The ideal mol% ration of Rb/Ba is presented, and optical damage sensitivity and lattice constant changes in optical waveguided layer are measuring. Experimental results show that the optical damage sensitivity is of (1.2～2.3)×10 -10 cm 2/J and independent of the constant of Ba and Heat treatment. Lattice constant changes Δc/c is in the range of 0.42%～0.25%, it decreased with increased additional constant of Ba.