A hydrocarbon isomerization method of making hydrocarbons containing at least 50 wt. % of saturated hydrocarbons having 7 and 8 carbon atoms (so-called heavy naphtha) come into contact, in the presence of hydrogen, with a solid acid catalyst containing a platinum group metal component supported on a carrier that contains as metal components at least one group IV metal component selected from the group consisting of titanium, zirconium and hafnium and at least one group VI metal component selected from the group consisting of tungsten and molybdenum. In particular, the isomerization method is preferably carried out at a temperature in a range of 190 to 250.degree. C. and a pressure in a range of 0.8 to 10 MPa and, as the catalyst, it is preferable to use a solid acid catalyst in which the carrier further contains aluminum as a metal component.