Abstract: Nonyldiphenylamine，an antioxidant，was synthesized by the reaction of diphenylamine with nonene under the catalysis of a solid superacid SO42-/TiO2. Several factors affecting the diphenylamine conversion and the selectivity for nonyldiphenylamine were investigated，including the calcination temperature of solid superacid，the reaction temperature and the amounts of catalyst，diphenylamine and nonene. The diphenylamine conversion reached to 97.3% with a selectivity for the aimed product，nonyldiphenylamine，of 86.4% when the superacid was calcinated at 550 ℃，where the reaction was carried out at 140 ℃ for 12 h with 3.50 g of catalyst，5.07 g of diphenylamine and 15.12 g of nonene. When the catalyst was reused for six times，the diphenylamine conversion still remained as 92.3% with the selectivity for nonyldiphenylamine of 80.2%. The catalyst deactivation mainly resulted from the carbon deposition and the loss of SO42-.