Chaohu Lake is one of the biggest freshwater lakes of China.This study was conducted to establish correlations between reflectance spectra and contents of chlorophy ll-a in Chaohu Lake, which was in eutrophic status.Reflectance spectra were measured during November, 2001 by using ASD FieldSpec HandHeld radiometer.Water samples for chlorophyll-a measurements and dominant algal species determination were collected at the same time.The features of the spectral reflectance of the lake were discussed.The correlation between the spectral ref lectance of single band and the contentof chlorophyll-a was low.The reflectance ratio of R_705nm/R_680nm and the reflectance first-derivative of 690nm were found to be significantly correlated with the contents of chlorophyll-a, and the r² gained using the reflectance ratio was higher than gained from the reflectance first-derivative of 690nm's.