Abstract: The effect of DL- malic acid on the floatability of muscovite was investigated under sodium oleate system, and the mechanism of DL-malic acid on muscovite was researched by means of FTIR and XPS spectra etc. The results show that floatability of muscovite can be prominently inhibited by DL-malic acid, because C₄H₅O₅^- and C₄H₄O₅^2- which from DL-malic acid solution could occur competitive adsorption with oleate ions in the pulp, and C₄H₅O₅^- and C₄H₄O₅^2- which adsorbed on muscovite surface aroused its surface zeta potential negative direction increase, which caused the electrostatic adsorption action of oleate ions in muscovite surface was weakened. Moreover, C₄H₅O₅^- and C₄H₄O₅^2- contain strong hydrophilic groups, these ions of which adsorbed on muscovite surface caused its surface had hydrophilicity, therefore the floatability of muscovite was inhibited.