Ru-added Ni catalysts supported on Al 2 O 3 or MgAl 2 O 4 were prepared and tested for the methane steam reforming to investigate the Ru-induced effects on the catalytic activity, the suppression of carbon deposition and the in situ self-activation of the oxidized catalysts during the reforming. The Ni catalysts promoted with a small amount of Ru (≤1wt%) showed a moderate reforming activity without a pre-reduction treatment using H 2 ; however, the Ni catalysts unpromoted with Ru were active only after reducing the catalysts with H 2 . Among the Ru-added Ni catalysts, the catalyst prepared by sequentially impregnating Ru by 0.5wt% over the calcined sample of 20wt% Ni/Al 2 O 3 showed higher reforming activity than the catalyst prepared by the co-impregnation of 0.5% Ru and 20% Ni over Al 2 O 3 . It was also revealed that the Ru doping greatly suppressed carbon growth on the Ni/Al 2 O 3 catalysts. Between the two support materials, MgAl 2 O 4 -supported catalysts were more active than Al 2 O 3 -supported catalysts. Most of the Ni on the MgAl 2 O 4 support were finely dispersed NiO clusters, while the Ni on the Al 2 O 3 support was hard-to-reduce NiAl 2 O 4 . The presence of Ru in a highly dispersed state appears to facilitate the reduction of such Ni-oxides and to decrease the coking propensity of the catalyst in the steam reforming of CH 4 .