We have studied the simultaneous absorption of gaseous mixtures of SO2 and O-2 in solutions of MnSO4 up to 0.75 mol/L and at temperatures between 10 and 40 degrees C. The reactor used was operated continuously for the gas phase and batchwise for the liquid. The liquid phase was saturated in SO2 at the first sampling after one hour. The absorption of O-2 was the controlling step in the process, with reaction order of 0 and 1 for SO2 and O-2, respectively, and a fast reaction regime for MnSO4 at concentrations of more than 0.025 mol/L. As far as manganese is concerned, our results show that the reaction order varies according to its concentration and we have obtained an equation which relates the kinetic constant to temperature and the concentration of the catalyst.