Oxine and alkyl oxine were used as scheelite modifiers in scheelite flotation and their adsorption mechanism was investigated. Electrokinetic and infrared studies on the pure scheelite and calcite surfaces have been carried out with oleoyl sarcosine, oxine, alkyl oxine and quebracho. These studies showed that alkyl oxine increases the negative zeta potential of scheelite to a less negative value whereas the negative zeta potential value of calcite was not changed with this reagent. On the other hand, zeta potentials of both calcite and scheelite became more negative upon treatment with quebracho. Conditioning af calcite and scheelite minerals individually with alkyl oxine before quebracho addition increased the flotation efficiency of oleoyl sarcosine in scheelite flotation but no changes occured in calcite flotation. Infrared studies also showed that, oxine and alkyl oxine were chemically adsorbed on the scheelite surface and not on the calcite surface.