This paper studies the influence of two pH modifiers, namely sodium hydroxide (NaOH) and sodium carbonate (Na2CO3), on the flotation of celestite ore using sodium oleate as the collector and quebracho as the depressant. Results show that, for the same experimental conditions (pH = 10.5, sodium oleate = 1500 g/Tm and low quebracho concentrations), the use of Na2CO3 provides enhanced recovery rates and concentration of celestite in the floated mineral, compared with NaOH.