Methylcyclopentane is ring-expanded to cyclohexane and cyclohexane is ring-contracted to methylcyclopentane on 12-tungstophosphoric acid (HPW) supported on silica and on stoichiometric microporous silver 12-tungstophosphate. The conversions of the two reactants increase with the loading of HPW on SiO2 while achieving significantly higher values on silver 12-tungstophosphate which pass through a maximum as the Ag/H+ preparative ratio increases. The ring-expansion and ring-contraction processes on the supported HPW and the microporous AgPW are catalyzed by the acidic protons in the solid acid and the residual protons in the silver salt.