Aromatic contaminants, 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chlorophenol (4-CP), were photocatalytically degraded in aqueous solutions under visible light illumination. 2,4-D was degraded more rapidly with more amount of simultaneous hydrogen generation than 4-CP. This is due to their difference in oxidative potentials, hydrophobic effects, electrostatic interactions and chemisorptions on the photocatalyst 3%WOx /TiO2.