Nanosized solid superacids SO/TiO and SO/TiO, as well as MCM-41-supported SO/ZrO, were prepared. Their structures, acidities, and catalytic activities were investigated and compared using XRD, N adsorption-desorption, and in situ FTIR-pyridine adsorption, as well as an evaluation reaction with pseudoionone cyclization. The results showed that SO/TiO and SO/TiO possess not only nanosized particles with diameters <7.0 nm, a BET surface greater than 140 cm/g and relatively regular mesostructures with pores around 4.0 nm, but also a pure anatase phase and strong acidity. Different from the Lewis acid nature of SO/ZrO/MCM-41, SO/TiO and SO/TiO exhibit mainly Br¢nsted acidities. The strongest Br¢nsted acid sites were produced on SO/TiO promoted with HSO, while Lewis acid sites on SO/TiO even stronger than those on SO/ZrO/MCM-41 were generated when persulfate solution was used as sulfating agent. Because of their distinct acid natures, SO/TiO and SO/TiO exhibited catalytic activities for the cyclization of pseudoionone that were much higher than that of SO/ZrO/MCM-41. It can be concluded that the existence of more Br¢nsted acid sites was favorable for proton participation in the cyclization reaction.