Photobleaching process and the resulting refractive index profiles of the nonlinear optical polymeric thin films have been investigated for the formation of active and passive waveguide devices. The material, a PMMA based copolymer with stilbene derivative as side chain, is formed to thin films by spin coating. Two different wavelengths of 458nm and 514.5nm generated from Ar+ ion laser are selected as the bleaching Light, which are located near the absorption maximum and the absorption edge of the material, respectively. Bleaching rate of the thin films measured by transmission experiment is found to be linearly proportional to the power of the incident light, indicating that the photobleaching is one photon process. Evolution of the refractive index profiles with bleaching time is obtained using the inverse WKB method with the measured guiding mode indices. The refractive index profiles bleached with 458nm are steeper than those bleached with 514.5nm as expected. A simple kinetic model with the parameters deduced from the transmission experiment is used to delineate the refractive index profiles and the resulting profiles are compared with the experimental ones.