Though aliphatic frothers used in industry were mostly in mixed form, fundamental understanding of mixed adsorption, especially the synergistic effects, remains unsatisfactory. In this study, the adsorption of MIBC, a popular frother with the branching structure, and 1-heptanol is investigated at air/water interface. In comparison with adsorption behaviour of straight chain alcohols reported in literature, the mixture demonstrated a special effect, which can be contributed of branching structure of MIBC. The experimental results were analysed mathematically using two theoretical models of Fairnerman and Siddiqui as well as an empirical model. The influence of branching structure on molecular arrangements in adsorption layer and flotation process is also discussed.