Kinetic parameters for the unimolecular thermal isomerizations of methylcyclopropane to four isomeric butenes have been determined from rate constant measurements over a wide range of temperatures, 695-1154 K, using a single-pulse shock tube and a static reactor. For the overall reaction, E-a = 64.4 +/- 0.3 and log(A, s(-1)) = 15.37 +/- 0.07, values consistent with earlier studies at lower temperatures. The measured rate constants for the isomerization to cis- and trans-2-butene give E-a = 63.3 +/- 0.3 and 64.9 +/- 0.3 kcal/mol, and log(A, s(-1)) = 14.60 +/- 0.07 and 14.75 +/- 0.06, respectively, values in good agreement with the thermochemically based predictions of O＇Neal and Benson. The similarity of kinetic parameters for the two reactions is consistent with the formation of the two 2-butenes through a common diradical intermediate. Kinetic data for 1-butene and 2-methylpropene formation an well represented by E-a = 64.5 +/- 0.5 and 66.4 +/- 0.2 kcal/mol and log(A, s(-1)) = 15.02 +/- 0.11 and 14.81 +/- 0.05. The higher E-a for 2-methylpropene formation compared with E-a for the production of 1-butene, and of cis- and trans-2-butene, is due to the higher energy required to break the C(2)-C(3) bond compared with the methyl-substituted C(1)-C(3) bond.