The effect of hydrogen on n-butane isomerization over Pt/SO42--ZrO2 and Pt/SiO2 + SO42--ZrO2 hybrid (physical mixture of Pt/SiO2 and SO42--ZrO2) was dependent on reaction conditions (temperature, hydrogen partial pressure). At high reaction temperature under low hydrogen pressure, the reaction order with respect to hydrogen was close to zero, but at low reaction temperature under higher hydrogen pressure, that of hydrogen was negative (-0.5 approx. -1.0). The inhibition effect of hydrogen on the activity may be caused by the hydride formed by the hydrogen spillover phenomenon. It was found that C4 olefins and C8 hydrocarbon were not reaction intermediates, and the reaction mechanism of n-butane isomerization is a mono-molecular mechanism. The reaction parameters were similar on Pt/SO42--ZrO2 and on Pt/SiO2 + SO42--ZrO2 catalysts. This suggested that the hydrogen effect is universal on the catalyst surface and that the proximity of Pt and acid site is not so important.