Nitrogen, isobutane, isobutylene and 2,2,3,3-tetramethylbutane are the only products found in the thermal decomposition of 2,2'-azoisobutane. They are the results of the direct free radical dimerization and disproportionation. Ratio of the rate constants of disproportionation to dimerization was found to be 1.9 at 268°C and 4.5% azobutane in helium. This compared with Blackham and Eatough's value of 1.4 at 243°C and 3.6 at 290°C with 4% azobutane in helium. The ratio of the disproportionation to dimerization increased with an increase in temperature. A change in contact time affected the ratio at lower reaction temperatures but had little effect on it at higher temperatures. The contact times used were between three and seven seconds. Research would be useful at lower contact times.