It was shown that the nature and method of the second element-modifier (Zn, Si, La, and Mg) introduction have a significant effect on the acidic properties of the zeolite catalysts and the active component (Rh) localization, which leads to a change in their catalytic properties in the oxidative methane carbonylation into acetic acid. The most active second components were Cu and Zn, introduced by impregnation (acetic acid yield was 919 and 819 μmol·gcat−1, respectively). Using temperature-programmed desorption of NH3, Fourier-transform infrared spectroscopy of pyridine adsorption and X-ray photoelectron spectroscopy it was found that an improvement of catalyst efficiency was associated with an increased acidity and a greater content of Brѳnsted acid sites together with an increase in the proportion of Rh atoms inside microporous channels and/or channel intersection voids, that are active in the acetic acid formation.