High concentration (1.3 vol.%) of 1-methylnaphthalene was selected as a tar model compound to investigate the catalytic conversion of tar from hot coke oven gas (COG) with lower steam content under atmospheric pressure over the Ni/MgO/Al2O3 catalysts. The catalysts were prepared by impregnating boehmite (AlOOH) with an aqueous solution of magnesium nitrate and nickel nitrate. The effects of Ni loading, reaction temperature, steam/carbon (S/C) molar ratio on the catalytic performance of the catalysts were discussed in detail. The catalysts exhibited excellent activity, stability and resistance to carbon deposition. Tar compounds could be completely converted into light fuel gases over 10% Ni/MgO/Al2O3 at 775 degrees C and S/C = 0.7. The effect experiments of sulphur were performed by adding 1000 and 2500 ppm H2S in the feed. The used catalysts were characterized by XRD and TG analyses. It was first found that addition of H2S in the feed could greatly inhibit the carbon formation on the catalyst surface and lead to significant improvement in the activity and stability of the catalyst. This phenomenon has never been reported previously in the tar steam reforming. (C) 2010 Elsevier B.V. All rights reserved.