The disagreement in the literature data on equilibrium concentrations in the mixture of butylenes was demonstrated, and their correct values were calculated. The temperature dependence for the equilibrium constant of the isomerization of n-butylenes into isobutylene was derived. It was shown that the product compositions achieved in the manufacture of isobutylene by the skeleton isomerization of n-butylenes can be close to the equilibrium ratios. The experimental results obtained on F/Al2O3 and Nb2O5/Al2O3 catalysts are given.