Abstract: strains of microorganisms which were found to produce flocculant were isolated from activated sludge. After rescreening, a strain Pseudomonas GX4-1 with high flocculating activity was obtained. The optimum culture conditions are:glucose 2%, yeast extraction 0.4%, KH2PO4 0.4%,30 , 200 r/min, cultivated for 23 days in flakes. The strain produces a strong-activity flocculant, with flocculating rate of 92.7% against kaolin clay suspension, under optimum flocculation conditions.