An investigation was made into the thermal decomposition of twenty-seven aliphatic acetates, using a micro-scale flow reactor connected to a gas chromatograph. The rate of elimination increases markedly as the degree of alkylation of the u-carbon atom becomes higher. The accelerating effect of B-alkyl substituents on the rate of elimination is small, as compared with that of a-alkyl substituents. The reactivity of the aliphatic acetates approaches a limiting value as the carbon chain is extended. The reactivity decreases on the introduction at the 8-carbon atom of an electron-attracting group and increases on the introduction of an electron-releasing group. A tentative mechanism is proposed which is based on the reversible formation of an ion-pair.