Thiosulfate ions are formed during processing of sulfide ores. They have a detrimental effect on flotation resulting in recovery and selectivity problems. In this work, removal/management of thiosulfate ions during flotation of a Cu-Pb-Zn sulfide ore was investigated and discussed in detail. Batch scale flotation tests were performed by using synthetic water samples of different chemical composition. Evaluation of froth stability, metal recovery and selectivity showed that presence of thiosulfate ions resulted in depression of the sulfide minerals. Oxidation of thiosulfate by hydrogen peroxide (H2O2) was applied to remove/minimize the adverse effects on flotation. H2O2 was added to process water and concentration of thiosulfate ion was decreased down to acceptable levels for flotation. H2O2 oxidized majority of thiosulfate ions to sulfate form. Increase in sulfate ion concentration influenced froth stability, but not the flotation performance which was restored after water treatment.