The hydrodenitrogenation of 1-naphthylamine was studied over a sulfided NiMo/Al2O3 catalyst between 300 and 350 degreesC. 1-Naphthylamine reacted to tetralin, naphthalene, 1,2-dihydronaphthalene and 5,6,7,8-tetrahydro-1-naphthylamine. To elucidate the reaction mechanism, the reactions of the intermediates 1,2,3,4-tetrahydro-1-naphthylamine, 1,2-dihydronaphthalene and 5,6,7,8-tetrahydro-1-naphthylamine were studied as well. The results show that 1-naphthylamine reacts through hydrogenation to 1,2,3,4-tetrahydro-1-naphthylamine, which reacts by NH3 elimination to 1,2-dihydronaphthalene. The latter molecule subsequently reacts by hydrogenation to tetralin as well as by dehydrogenation to naphthalene. In addition, naphthalene is formed by direct denitrogenation from 1-naphthylamine. This direct denitrogenation may take place by hydrogenation of 1-naphthylamine to 1,2-dihydro-1-naphthylamine, followed by NH3 elimination or followed by a Bucherer-type NH2-SH exchange, dehydrogenation and C-S bond hydrogenolysis.