MoO x and Ni–MoO x catalysts with maximum pore diameter at ca. 4.1 nm in the meso-pore range were prepared by reducing MoO 3 or NiO doped MoO 3 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 x is predominantly composed of the MoO x H y and MoO 2 phase. The former can be considered to be more active than the latter. Over the MoO x 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 MoO x catalyst lacks active sites with a metallic character for dehydrogenation–hydrogenation step in n-heptane isomerization. The Ni–MoO x catalysts have a lower specific surface area than the MoO x catalysts, due to that the reduction of MoO 3 was accelerated by nickel, and the fact that more H 2O was produced in the initial reduction process, this leading to MoO x sintering. Comparing with MoO x catalysts, the 5% Ni–MoO x 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.