The mechanism of hydrogen oxidation on a platinum-loaded gas-diffusion electrode has been investigated. Experimental potential–current curves, especially in the low overpotential range, have been measured for H2–N2 mixtures with a small content of hydrogen and for pure H2. Theoretical relations have also been presented. Comparing the experimental and theoretical relations, it is concluded that the hydrogen oxidation occurs according to the Volmer–Tafel mechanism. The reactivity of the electrode has a large effect on the kinetic parameters for hydrogen oxidation. The limiting current is determined by diffusion of hydrogen for a very reactive gas diffusion electrode and by the Tafel reaction for a gas diffusion electrode with a low reactivity. The transfer coefficient for the Volmer reaction V is 0.5 and i0,V/i0,T 0.1 for a very reactive gas diffusion electrode. V increases and i0,V/i0,T ratio decreases with decreasing reactivity of the gas diffusion electrode.