Abstract: A bioflocculant MBF-18 with high flocculating activity was produced by Pseudomonas fluorescens strain JX18. Measurements of chemical analysis，UV and IR spectroscopies revealed that the bioflocculant MBF-18 is mainly composed of polysaccharides and distributed in the fermentation broth. Flocculation property study showed that MBF-18 has a high thermal stability and a wide pH serviceable range. The flocculating activity showed no decrease even at 100℃and kept stable with higher than 85% at pH 3.0—10.0. Further investigation revealed that the optimum concentration of this bioflocculant for flocculation was 2.5 mg/L，and CaCl2 was proved to be the best coagulant aid with an optimum concentration of 0.5 g/L. Scanning electron microscopy image of the solid-state MBF-18 showed that the bioflocculant has a linear morphology，and connected with Kaolin clay molecules upon flocculation.