In the vapor phase nitration of benzene with diluted nitric acid, we have succeeded in keeping a high nitration activity of the supported sulfuric acid catalyst for more than 2 months by co-feeding a trace amount of sulfuric acid (H2SO4/HNO3 = 1/5000 (wt. ratio)). The results after 60 days on-stream over 10 wt.%-H2SO4/SiO2 catalyst are as follows: yield of nitrobenzene (NB), 93% based on KNO3; selectivity of NE, 97% based on HNO3; productivity of NE (STY), 0.76 kg/kg cat h. These performances were demonstrated in bench scale experiments using molded silica or quartz supports. Finally, nitration reactions of toluene and chlorobenzene were conducted and compared with each other over several solid acid catalysts developed by us.