Temperature effects in dealkylation and isomerization of dialkylbenzenes at the temperature range of 200 to 500 °C have been discussed from the viewpoint of linear free energy relationships (LFER). The effects of the second substituents on both reactions are well described by the Hammett law. The alkyl shift reaction, which is defined as the migration of an alkyl group in one direction on a monosubstituted ring, has been compared with the dealkylation of monoalkylbenzenes. The preexponential terms in both reactions have been shown to be constant independent of alkyl groups, whereas the activation energies are 24.8, 19.5, and 15.6 kcal/mole for the dealkylation of Et, isoPr, and tert-Bu groups, respectively, and 17.8, 14.1, 10.6, and 8.96 kcal/mole for the alkyl shift reaction of Me, Et, isoPr, and tert-Bu groups, respectively. The LFER equations for isomerization and dealkylation have been further extended over the temperature range of 200 to 500 °C, as follows: k i(R 1, R 2,T)= ∑ R w(r)k i(0, ∞) exp [− {γ′ iΔH c +(R)+E A, i(0)} RT ]+2.3ρ(R)σ(R f )] where the Hammett ϱ values are assumed to be practically independent of temperature. The generalized equation given above for dealkylation and isomerization has made it possible to predict the selectivity between two reactions of any kind of dialkylbenzenes. The reaction mechanism of both reactions proposed in a previous paper has been refined on the basis of the LFER found in the present work.