A novel reagent, guar gum (GG), is investigated as the depressant on the depression of chalcopyrite and jamesonite, when mixed aerofloat (CSU11) is used as the collector in flotation tests. Kinetics, dynamic potential, adsorption and infrared spectra analysis are performed to study the interaction mechanism between GG and minerals. The flotation results display that selective flotation separation of chalcopyrite from jamesonite is achieved under conditions of depressant GG 2.5 mg/dm3, collector CSU11 10 mg/dm3 and frother MIBC (Methyl isobutyl carbinol) 10 mg/dm3 at pH 5.3. As to mixed minerals flotation, the Cu grade and recovery in the concentrate is 21.35 % and 85.12 %, respectively, indicating that GG has a selective depression effect on jamesonite. Flotation kinetics shows that the addition of GG can dramatically reduce the floatability of jamesonite but hardly influences that of chalcopyrite. The zeta potential and adsorption reveal that the depressant GG adsorbs strongly on the surface of jamesonite. Infrared spectra reveal a dominant chemisorption between GG and jamesonite, while GG occurs weak chemisorption on chalcopyrite surface. This is the reason why GG has excellent selectivity for jamesonite and less effect on chalcopyrite.