Abstract: A water-stable ionic liquid 1-butyl-pyridinium hydrosulfate has been synthesized,and it has been checked by FTIR and TGA.Then it was used as a catalyst to catalyze fatty acids of Jatropha curcas L.seed oil for biodiesel.It showed that the yield was more than 96%,under the conditionstemperature 100℃,mass percentage of the catalytic relative to fatty acids 6%,V(methanol):V(fatty acids)=1:1,and time 75 minutes.The ionic liquid was stable.After six times recycling,it still remained high catalytic conversion rates.