The thermal decomposition of methylcyclohexane in the presence of steam was studied in a laboratory tubular reactor with large inner surface at atmospheric pressure. Experimental data were obtained at a temperature range of 700-790 OC and at residence times of 0.04-0.20 s. The overall kinetic analysis gives a value of 201.3 kJ mol-' for the activation energy and 0.532 X 10" s-' for the frequency factor. The pyrolysis products (more than 90) were identified with capillary gas chromatography by comparison of their retention indices with those of standard hydrocarbons and by mass spectrometry