Photo-degradation of 4-chloroaniline (4-CA) in aqueous solutions was studied by UV irradiation. The degradation efficiency of 4-CA and total organic carbon (TOC) removal were investigated by changing the irradiation UV wavelength, initial concentration of 4-CA, pH value, adding H,2,O,2, and saturated with different gases in the photo-degradation experimental system. The results show that the photo-degradation of 4-CA is very effective, with removal rates at about 99% and 50% of 4-CA and TOC, respectively, after 1 hour irradiation time when 10mmol/L H,2,O,2, was added to 1mmol/L 4-CA aqueous solution and saturated with air, which implies that the UV irradiation technique might be a promising process for the treatment of 4-CA waste effluents.