The photobleaching process of an electro-optic polymer, a PMMA-based side-chain polymer with the non-linear optic (NLO) chromophore DANS, has been investigated with irradiation only, with poling only, and with both irradiation and poling in that order or in the reverse order. The photobleaching was carried out using the near-UV lines. FTIR spectra and UV-Vis absorption spectra were obtained after each irradiation. Refractive indices and electro-optic coefficients were measured in the photobleaching processes. The results suggest that the photobleaching processes result from the photo-oxidation of the NLO polymer.