The optimal conditions of production of flocculant by the culture of Flavobacterium sp. were examined, using molasses wastewater to replace glucose as carbon source and energy source in the culture medium. Results showed that the COD concentration in molasses wastewater favorable for the growth of the Flavobacterium sp. was 5000 mg•L-1, and inoculum size of 5%(v/v), 30°C, initial pH 7.0 and shaking speed of 150 r•min-1, under the optimal culture conditions, the highest flocculating activity achieved for Kaolin suspension was 95.0% and 4.0 g biomass /L broth was obtained. The Flavobacterium sp. biomass was effective in flocculating some soluble reactive dyes in aqueous solution, reactive Light-Yellow K-4G with a decolorization efficiency of 98.5, using 20 mL of the flocculant in 500 mL of 100 mg•L-1 dye solution.