The photodegradation of reactive green KE-4BD solution is investigated using N-doped titania (N-TiO2) under visible light irradiation. N-TiO2 is prepared using ammonia or urea as a nitrogen source and characterized by X-ray diffraction, Brunauer-Emmett-Teller methods, and UV-visible diffuse reflectance spectra. The effects of the initial dye concentration and pH on photocatalytic degradation are studied, and the direct correlation between pH, dye concentration, and the rate of degradation are determined. Experimental results show that aqueous solutions of KE-4BD degrade easily in weakly acidic conditions in the presence of N-doped TiO2 (1 g/L) as a photocatalyst. The optimized dye concentration for photolysis is 150 mg/L. The complete degradation of KE-4BD could be achieved under visible light irradiation, and the dye molecules could be partly decomposed into inorganic substances.