The effect of catalyst length and hydrogen addition on the combustion characteristics of n-butane in a catalytic Swiss-roll combustor was studied experimentally. The results show that the 4.5-mm ceramic with Pt catalyst slightly outperforms the 3.0-and 6.0-mm ceramics. However, changing only the catalyst length does not expand the lower flammable limits to lean fuel. Further experiments on the combustor with the 4.5-mm ceramic show that the addition of hydrogen to flammable mixtures can expand the lower flammable limits of such mixtures to lower than 0.5. Analyses on exhaust gas and stable combustion temperature indicate that hydrogen supplies heat through complete combustion and enhances the n-butane conversion ratio. A high amount of hydrogen is favorable for flammable range expansion. Moreover, a higher amount of hydrogen can further reduce the lower limits.