Strong toluenesulphonic and triflic acids were incorporated into MIL-101 chromium(III) terephthalate coordination framework producing hybrid proton-conducting solid electrolytes. These acid@MIL hybrid materials possess stable crystalline structures which do not deteriorate during multiple measurements or prolong heating. Particularly, the triflic-containing compound demonstrates the highest 0.08 S•cm-1 proton conductivity at 15% RH and temperature 60 °C, exciding any today's commercial material for the proton exchange membranes. The structure of the proton-conducting media, as well as the long-range proton transfer mechanics were unveiled, in a certain respect, by FT-IR and 1H-NMR spectroscopy investigations. The acidic media presumably constitutes large separated droplets, coexisting in the MIL nanocages. One component of the proton transfer appears to be related to the facile relay (Grotthuss) mechanism through the extensive H-bonding interactions within such droplets. The second component occurs during a continuous reorganization of the droplets, thus ensuring the long-range proton transfer along the porous structure of the material.