MOOx and Ni-MoOx catalysts with maximum pore diameter at ca.4.1 nm in the meso-pore range were prepared by reducing MoO3 Or NiO doped MoO3 in H-2 flow at 623 K in a period of 6-12 h. The catalysts were used in n-heptane isomerization isothermally carried out at 573 K under atmospheric pressure in a conventional fixed-bed flow reactor. MOO, is predominantly composed of the MoOxHy and MoO2 phase. The former can be considered to be more active than the latter. Over the MOO, catalyst, the H-2 partial pressure positively affected the reaction rate with an order of ca.0.35. It can be deduced from the result that the MoOx catalyst lacks active sites with a metallic character for dehydrogenation-hydrogenation step in n-heptane isomerization. The Ni-MoOx catalysts have a lower specific surface area than the MOOx catalysts, due to that the reduction of MoO3 was accelerated by nickel, and the fact that more H2O was produced in the initial reduction process, this leading to MoOx sintering. Comparing with MoOx catalysts, the 5% Ni-MoOx catalysts are more active in terms of the reaction rate per unit surface area of the catalyst, the explanation is that the dehydrogenation-hydrogenation step in n-heptane isomerization is effectively enhanced by incorporation of Ni in the catalysts. (C) 2004 Published by Elsevier B.V.