PURPOSE: To prepare nitrobenzene, in high yield, by the vapor-phase nitration of benzene with a nitrating agent using a catalyst comprising a solidified acid obtained by impregnating sulfuric acid in a solid carrier and calcining the product.

CONSTITUTION: The objective nitrobenzene is prepared by the vapor-phase nitration of benzene with a nitrating agent selected from NO2 and N2O4, using a catalyst comprising a solidified acid obtained by impregnating sulfuric acid in a solid carrier (e.g. silica.alumina) in an amount of 5W50wt%, and calcining the impregnated product at 100W400°C. The vapor-phase nitration reaction is preferably carried out at 100W300°C, using 0.1W3 moles of the nitrating agent per 1 mole of benzene, and using an inert gas such as nitrogen as a diluent. The catalyst exhibits extremely high catalytic activity compared with the conventional silica gel catalyst and a phosphate-type catalyst, and scarcely yields the by-products such as dinitrobenzene.