Carboxymethyl cellulose (CMC) has been widely used as a flotation depressor. In this study, it showthat the CMC is also an effective depressor for ilmenite and titanaugite flotation by the results of monomineral floatation tests. In order to find out the depression mechanism of the CMC, Zeta potential tests are carried out, and the results showed that after adsorption of CMC on ilmenite and titanaugite, the Zeta potentials of the minerals significantly decreased. It found that the adsorption of CMC on ilmenite and titanaugite reaches its maximum at pH 5, and the adsorption capacity of titanaugite to the CMC is greater than that of ilmenite. According to the investigation result, it must be a competitive adsorption between ilmenite and titanaugite.