Abstract: Brønsted acidic ionic liquid BPYHSO₄ was synthesized and characterized by FT-IR and ¹H-NMR. BPYHSO₄ was then used as a catalyst in alkylation desulfurization of FCC gasoline; the effects of the reaction temperature, time and mass ratio of ionic liquid to oil on the desulfurization efficiency and FCC gasoline quality were investigated. The results showed that after reaction for 90 min under 65 ℃ and an ionic liquid to oil mass ratio of 0.09, the sulfur content of FCC gasoline is decreased from 580.0 to 6.4 μg/g, with a desulfurization rate of 98.90%, which can meet the request of Chinese National Standard V for the sulfur content in motor gasoline (< 10 μg/g). A survey on the distribution of sulfur compounds indicated that sulfur compounds are transferred from light fraction (< 170 ℃) to heavy fraction (> 170 ℃) with the help of BPYHSO₄ and the sulfur compounds in heavy fraction can then be removed further by hydrodesulfurization. PONA results indicated that the alkylation desulfurization catalyzed by BPYHSO₄ has little effect on hydrocarbon composition and octane number of FCC gasoline. Moreover, the BPYHSO₄ ionic liquid can be recycled through extraction and reused in the alkylation desulfurization.