A three-electrode system composed of TiO2/Ni as the working electrode, porous nickel as the counter electrode, and saturated calomel electrode (SCE) as the reference electrode was used for the photoelectrocatalytic degradation of organic compounds. The photoelectrocatalytic degradation of sulfosalicylic acid (SSal) under anodic bias potential was investigated. It is shown that SSal can be degraded effectively as the external potential is increased up to 700 mV (vs SCE). The characteristics by electrochemical impedance spectroscopy (EIS) of the photoelectrocatalytic degradation of sulfosalicylic acid (SSal) was also investigated. It is shown from the EIS that the photoelectrocatalytic degradation appears to be a simple reaction on the electrode surface, suggesting that only one step of charge transfer is involved in the electrode process. The value of the resistance of charge transfer for the photoelectrocatalytic reaction of SSal manifests itself not only in the reaction rate, but also in the separation efficiency of the photogenerated electron-hole pairs. The separation efficiency of the electron-hole pairs under N2 atmosphere is higher than that under O2 atmosphere.