The depression effect of corn starch on the surface of muscovite mica powder at different pulp pH value was investigated. The experiments were performed on single mineral, and its flotation performance was studied by flotation tests, adsorption quantity measurement, zeta-potential technique and Fourier transform infrared (FT-IR). The results indicated that the depression effect was varied with the pulp pH value when dodecylamine chloride (DDA) was used as collector, the strongest inhibitory effect appeared at pH 2 and the zeta-potential of muscovite mica increased overall after conditioned with corn starch solution. It was confirmed by the FT-IR spectra that the corn starch indeed adsorbed on the surface of muscovite mica powder and physical adsorption was occurred between muscovite mica and corn starch. This study leads to a better understanding of the depression effect of corn starch on the surface of muscovite mica powder.