The properties of the Mn–Ce/Beta zeolite catalyst in the selective catalytic reduction (SCR) of NO x have been investigated. The introduction of Ce leads to a marked increase in the NO x conversion at 100–250°C. The data of this study are consistent with the “bifunctional” pathway of SCR suggested for Mn/Beta, which consists of two stages—NO oxidation to NO2 over the oxide component and “fast” SCR over the zeolite. The increased activity of Mn–Ce/Beta at the NO-to-NO2 oxidation stage is due to the formation of MnCeO x mixed oxides enhancing the mobility of lattice oxygen. The determining role is played by the activity of the zeolite component in the “fast” SCR reaction.