A novel organic compound acetic acid-[(hydrazinylthioxomethyl)thio]-sodium was synthesized and characterized. The flotation performance and adsorption mechanism of AHS to galena were investigated by micro, bench flotation tests, UV spectra, zeta potential, FTIR and XPS measurements. The results demonstrated that AHS exhibited superior depressing power to galena and could be used as selective depressant for flotation separation of molybdenite from galena. The results of UV spectra, FTIR, zeta potential and XPS measurements demonstrated that AHS chemisorb on galena surface by forming five-membered cheat ring with releasing of H ions. Therefore, the possible adsorption mode of AHS on galena surface was recommended.