The adsorption of a heterocyclic thioamide (such as 2-mercaptobenzothiazole (MBT) collector) on pyrite has been studied. 2-mercaptobenzoxazole (MBO) and 2-mercaptobenzimidazole (MBM) were used in the tests as references. The flotation of pyrite with MET, MBO, and MBM has also been investigated. Quantum chemical calculations carried out by the extended Huckel method for adsorption models, MBT ion-pyrite and MBT dimer-pyrite, are used to illustrate the electronic, binding and energy states of the two adsorption systems. It is demonstrated that MBT ions can be chemically adsorbed onto the pyrite surface by the formation of bonds between sulphur and nitrogen atoms of MBT and iron atoms on the pyrite surface. The adsorption of MBT dimer is more stable than that of MBT ion on pyrite. The adsorption of MBT on pyrite is further discussed in terms of the adsorption model of MBT ions onto the pyrite surface with hydrogen and hydroxyl ions previously adsorbed.