The phosphate rock flotation test was carried out using Escherichia coli (E. coli) as a depressant of dolomite. The results showed that E. coli had a great selective depression on dolomite during flotation. With E. coli as a depressant of dolomite, a useful beneficiation index of phosphorus concentrate with P₂O₅ grade of more than 30% and MgO content less than 1.2% can be obtained by closed-circuit of one-stage roughing and one-stage cleaning. Furthermore, the depression mechanism of E. coli was studied by adsorption experiments, infrared spectrum, and zeta potential. This study shows that the adsorption ability of E. coli onto dolomite is stronger than that of collophanite. When the pH is greater than 6, E. coli are chemically adsorbed on the surface of the collophanite and dolomite,which also increases the negative charge on the surface of the two minerals. The selective adsorption of E. coli cells to dolomite was best when the pH value is about 7.8.