The degradation of acid orange 7 dye (AO7) was studied using a 1 L semi-batch tank stirred glass reactor for performing three different photochemical processes (photoperoxidation, Fenton, photo-Fenton). A commercial low pressure lamp was used for irradiation of samples. The advancement of degradation was monitored by measurement of color reduction, UV-spectra, HPLC-UV and COD. The obtained results showed that the photo-Fenton treatment was the most effective for the degradation of AO7.