To provide a method for isomerization of a hydrocarbon mixture containing 7C and 8C saturated hydrocarbons (so-called heavy naphtha).

A hydrocarbon mixture containing at least 50 wt.% of 7C and 8C saturated hydrocarbons is brought into contact with a solid acid catalyst comprising a sulfuric acid component and platinum-group metal component, carried on a carrier containing a zirconia part and alumina part, in the presence of hydrogen at a reaction temperature of 130-160°C. The solid acid catalyst preferably used comprises one of which the zirconia part contains a tetragonal crystal zirconia, the alumina part contains γ-alumina, and the platinum-group metal component is crystallized.