Researches on optical properties of Chromophoric Dissolved Organic Matter (CDOM) has played an important role in quantitative water-color remote sensing retrieval. The optical properties of CDOM in coastal waters of Lake Taihu were investigated from June 10 to June 18 in 2007. The results show that the specific absorption coefficient of CDOM varied significantly and was higher apparently in Gonghu Bay than in other areas. The specific absorption coefficient at 440nm (ag(440)) also showed a similar trend, and it reached the highest value in Gonghu Bay. The ag(440) in waters of Meiliang Bay, Zhenhu Bay and Guangfu Bay also showed an increased trend. On the contrary, the spectral slope coefficient (Sg) in Gonghu Bay was lower than others, and showed a better correlation with ag(440), while Sg in other bays was higher and showed a poor correlation with ag(440). The results demonstrated that it is important to learn the optical properties of CDOM in Lake Taihu, which would then allow higher precision in remote sensing applications