In this paper, the separation of arsenopyrite from chalcopyrite, pyrite, galena with organic depressants (guergum and sodium humic) was discussed, and the functioning mechanism of those organic depressants discussed. The experimental results of monomineral flotation indicated that both guergum and sodium humic have depressing effect on arsenopyrite in the presence of ethyl xanthate. Guergum and sodium humic showed different depressing ability to pyrite, chalcopyrite and galena, and the higher the pH-vualue in pulp, the stronger the depressing ability. Ultraviolet-Visible Spectrophotometric study showed that the adsorption layer of xanthate on surface of minerals had been desorbed by the two organic depressants, and the selective desorption of the collector layer was found from different minerals. The xanthate cover on minerals surface was set free when dosage of the organic depressants was high enough. For artificially-mixed minerals, the separation of arsenopyrite from other sulphides was successfully realized by controlling dosage of the organic depressants. And sodium humic had been used successfully to decrease arsenic content in sulphide concentrates in a commercial Lead-Zinc concentrator.