In this work, the effects of different factors on the flocculating activity and flocculation mechanism of bioflocculant XMMBF from Bacillus lichgniformis are investigated.. The results show that the optimum concentration,of bioflocculant for kaolin clay sedimentation is 4 mg/L. Both, monovalent and bivalent cations increase the floculating-activity, whereas trivalent cations inhibit it. The optimum pH and concentration of kaolin clay suspension are 5-11 and 2-10 g/L, respectively. adsorption of XMMBF on kaolin clay is described using the Langmuir adsorption model. Infrared spectrum,shows the carboxyl groups, amino groups, and hydrogen bonds in XMMBF prefer the flocculation process. The zeta potential of kaolin clay can he changed from -26.26 to -1.08 mV by both Ca2+ and XMMBF. The formation of ionic bonds in the floc can be related to its sensitivity to HCl. Finally, through the help of SEM pictures, the flocculation mechanism of XMMBF Is proposed.