Laboratory experiments were conducted to investigate the effect of ceramic-treated water on the inhibition of algal growth. The growth of Scenedesmus quadricauda and Chlorella vulgaris was enhanced by the ceramic-treated water in Allen medium containing high concentration of nutrients, but inhibited in natural water containing low concentration of nutrients. The growth of Oscillatoria tenuis and Microcystis aeruginosa was inhibited in both Allen medium and natural water. When comparing the effects of ceramic-treated water 1 (NC1) and 2 (NC2), the growth of O. tenuis and M. aeruginosa was somewhat enhanced by NC1, whereas inhibited by NC2. Therefore, it is suggested that NC2 can be more effective than NC1 in controlling the algal growth.