This paper describes the photocatalytic degradation of 4-chlorophenol using titanium dioxide (TiO_2) catalysts prepared in our laboratory. Pure TiO_2 powders were prepared using a modified thermal hydrolysis method involving the addition of either sulfate or aqueous ammonia to enhance the spontaneous precipitation of TiO_2. The continuous measurement of degrading 4-chlorophenol was made using a high performance liquid chromatographic method. The structure of the crystallized catalysts was a pure rutile structure and the particle size was 35-50 nm. The TiO_2 catalyst prepared using NH_4OH or H_2SO_4 exhibited the superior efficiency at degrading 4-chlorophenol to that prepared following the addition of distilled water. The catalyst prepared by adding NH_4OH shows similar efficiency to that of commercial catalysts, P-25 and ST-21, removing of 85% of original 4-chlorophenol within 6 h and 97% of it within 11 h. In addition to their simplicity and improved efficiency at degrading 4-chlorophenol, the method also alleviate the volatile organic problem commonly associated with this product.