Abstract: Flotation responses of rutile in various systems of sodium benzohydroxamide (BHA) combined with several fatty acid salts collectors were studied and the interaction mechanisms of the reagents, as well as that of the reagents onto the mineral have been studied using various measurements, namely, Zeta potential, surface tension, contact angle and UV diffuse reflectance spectroscope. The results indicate that the collecting ability (recovery) of the single reagent follows the order: sodium linolenate (89.23%) > sodium linoleate (69.57%) > sodium benzohydroxamide (38.43%) ≫ sodium stearate (7.13%). The number of the double bond in sodium salts of fatty acids bearing the same length of hydrocarbon chain has a significant influence on the reagent collecting ability and the synergistic effect of reagent combination, however, the deep reason is that the double bond has an important impact on such properties as Krafft point, molecular structure of fatty-acid collector as well as the interactions of fatty-acid collectors with BHA. The collecting ability of the three reagent combinations is sodium benzohydroxamide + sodium linoleate(SL) ≈ sodium benzohydroxamide + sodium linolenate (SN) ≫ sodium benzohydroxamide + sodium stearate (ST). It is observed that there is an electron conjugation effect among the double bonds in fatty-acid collector and the benzene ring in BHA which is the main reason for the formation of the association complex between the reagents. The amount and the configuration of the complexes could be critical for the collecting performance of reagent combination.