The rates of the thermal decomposition of t-butyl methyl ether have been measured in the range 433-495º. The reaction products are isobutene and methanol, and the kinetic form is first order. The Arrhenius equation K1 = 1014.38exp(-61535/RT) sec-1 describes the variation of rate with temperature. The reaction behaviour is consistent with a unimolecular mechanism. Comparison of the results with those obtained for the production of isobutene from various t-butyl compounds indicates that the reaction has some degree of heterolytic character.