In this study, the effects of anionic/cationic collector mixtures on surface tension () were investigated as a function of pH using the pendant drop method. For the tests, long-chain tallow amine and petroleum sulfonate, which are the most common anionic and cationic flotation collectors, were used individually and as binary mixtures with different mixing ratios. The results show that pH of the solution had crucial effects on surface tension values of the amine whose species distribution varied with pH but not on petroleum sulfonate that is found in the ionized form over the entire pH range. In the case of binary anionic/cationic collector mixtures, the minimum surface tension values were obtained under highly acidic pH conditions with a mixing ratio of 1:3, while the collector mixtures with 3:1 and 1:1 mixing ratios displayed similar surface tension values at all pH values. For all binary-collector mixtures with different mixing ratios, the surface tension values were found to be higher than those of single-collector solutions with equal collector concentrations. In the case of microflotation tests, the flotation recoveries of quartz in the presence of the binary anionic/cationic collector mixtures dropped more than 25% when compared with the results in the presence of single-collector solutions having equal collector concentrations.