S-N co-doped anatase nanosized TiO2 photocatalyst was successfully prepared by simple sol-gel method. The samples were characterized by XRD, XPS, UV-Vis. From the results of UV-Vis, a red shift of the absorption edge was brought out owing to the S and N codoping. XPS and UV-Vis studies revealed that N and S were in situ codoped in the lattice of TiO2 and the absorbance in visible light region decreased with the calcination temperature increased. The photocatalytic activity was evaluated by the photocatalytic oxidation of penicillin solution under visible light irradiation. The results show that visible-light induced photocatalytic activities of the as-prepared TiO2 powders were improved by S-N copoing. The high activity of S-N co-doped TiO2 can be related to the results of the synergetic effects of strong absorption in the UV-Vis region, red shift in adsorption edge.