Abstract: The effect of postprocessing (annealing and secondary ion exchange process) on the transmission characteristics of planar optical waveguide of a new Er3+/Yb3+codoped phosphate glass was investigated. Because of the redistribution of Ag+ ions under the annealing and difference of Ag+ ion concentration between glass waveguide surface and substrate, it is found that with the prolonging of annealing time and increasing of annealing temperature, the quantity of optical waveguide modes and the depth of waveguide are increased, and the difference of refractive index between surface and substrate are decreased. The annealing diffusion depth is in direct proportion to the square root of annealing time. The result of microprobe analysis indicates that buried optical waveguide was formed after the secondary ion exchange process, the profile was close to quadratic distribution and the buried waveguide contributes to the decrease of transmission loss of the optical waveguide.