For waters of Meiling Bay, Taihu Lake, field measurements were carried out Aug. 16, 2006, March 28 and Nov.12,2007. These measurements included diffuse attenuation coefficient of downwelling irradiance, absorption coefficients of pigments and non-pigments (aph and ad, respectively), and the colored dissolved organic matter (aCDOM), and backscattering coefficients (bb). For the total of 15 stations that have Kd, aph, ad, aCDOM, and bb, it is found that the primary contributor to Kd is absorption coefficient. bb does contribute to Kd, but in a minor role. Also, it is found that this relative significance in contributing to Kd varies seasonally. In March, the order of major to minor contributors was ad, aCDOM, and aph, and then bb. In August, this order became aph, ad, aCDOM, and then bb. It is more complicated in November, as at 440 nm, the order is ad, aph and aCDOM, and bb; at 595 nm, the order is ad and aph, bb, and aCDOM; at 676 nm, however, the order became aph and ad, bb, and then aCDOM.