For pretreatment of selective flotation, plasma treatment of chalcopyrite and molybdenite was applied then the minerals were washed by solution at pH 9 with oxygen bubbling. Surface characteristics of these minerals were investigated with AFM, XPS, zeta potential and contact angle measurements. Contact angle of chalcopyrite and molybdenite decreased a lot by plasma treatment. When they were washed with pH 9 solution with oxygen bubbling, contact angle of molybdenite increased whereas chalcopyrite one kept low. Adhesion force measurements indicated similar behavior. Result of flotation experiments indicated low recovery of both chalcopyrite and molybdenite after plasma treatment and only molybdenite recovery became higher after washing. Selective flotation of chalcopyrite and molybdenite could be achieved with this process. However, flotation of mixture of chalcopyrite and molybdenite after these treatments indicated both chalcopyrite and molybdenite were depressed. Addition of emulsified kerosene changed the flotation results where molybdenite was floated and chalcopyrite was depressed. Possible mechanism of selective flotation was proposed from the results of XPS, AFM, etc. (C) 2014 Elsevier Ltd. All rights reserved.