This is the first report indicating the Pd clusters filled in multi-walled carbon nanotubes (MWNT) as catalyst applied in liquid phase benzene hydrogenation. The treatment of MWNT, filling of metals, the effects of the filling amount of palladium, evaluation of catalytic property, and the comparison with various conventional supports were investigated. The experiment results indicated that the Pd clusters filled in the inner of carbon nanotubes exhibited higher activity than other supports such as Y zeolite and activated carbon. According to various characterizations, the relationship between catalytic activity and the structure of the carrier was briefly discussed. (C) 2004 Elsevier B.V. All rights reserved.