The inhibition of freshwater algal growth was investigated using powdered TiO2 as a photocatalyst under artificial sunlight irradiation with a combination of fluorescent lamp and black light in order to develop a new method of water quality improvement in lakes or reservoirs using natural energy. The growth of Microcystis aeruginosa, Anabaena solitalia and Coelastrum astroideum was effectively inhibited by using powdered TiO2 photocatalyst at a concentration of 100mg·l-1, whereas that of Fragilaria capucina wasn't.