Abstract: A strain of bioflocculant-generating bacterium, named G-420 was isolated from activated sludge. The flocculating property of MBF-420 produced by flocculant-generated bacteria G-420 was studied. It was shown that the bioflocculant was an extra-cellular production and the flocculating active components were mainly distributed in the fermentation broth. MBF-420 had good flocculating capability and could achieve the flocculating rate of 95.99 % for kaolin suspension at a dosage of 2.4 mg·L-1. Meanwhile, MBF-420 was heat-stable, while it was kept in boiling water for 30 min, the flocculating rate was still retained above 93%. It also could keep high flocculating activity in a wide range of pH from 1 to 10, and the best flocculating activity was attained when the pH value was 4. The addition of metal ion could increase the flocculation rate and Ca2+ was the best metal ion. It also presented a good flocculating effect on different suspensions.