We are attempting to supply a new insight on interaction between Na+/K+-ATPase and H2O2. We demonstrate that in vitro the Na+/K+-ATPase, a non hemeprotein, is able to disproportionate H2O2 catalatically into dioxygen and water, as well as C-40 catalase. By polarography, we quantify O-2 production and by Raman spectroscopy H2O2 consumption. A comparative analysis of kinetics parameters relative to O-2 production shows that for Na+/K+-ATPase the affinity of the catalytic site able to transform H2O2 into O-2 is twice weaker than that for C-40 catalase. It also shows that the molar activity for O-2 production is 300-fold weaker for ATPase than for catalase. Inhibitors, pH and GSH studies highlight the differences between the heme-and nonheme-proteins. Indeed, for C-40, NaN3 is strongly inhibiting, but much less for ATPase. The pH range for the catalatic activity of ATPase is wide (6.5 to 8.5), while it is not for C-40 catalase (optimum at pH 8). The Na+/K+-ATPase catalatic activity is reduced in presence of glutathione, while it is not the case with C40 catalase.