Abstract: Basic ionic liquid N-methyl-N-butyl morpholine hydroxide (NbmmOH) was synthesized by two-step methods with N-methyl morpholine, N-butane bromide and potassium hydroxide as the materials. The chemical structure and thermal stability of the basic ionic liquid NbmmOH were characterized by FT-IR, elemental analysis and TGA; its solubility and catalytic performance in the esterification of oleic acid with methanol were investigated. The results showed that the basic ionic liquid has a good thermal stability; it is stable at a temperature above 200℃. The ionic liquid NbmmOH is soluble in the solvent of strong polarity and the solution in water exhibits strong alkalinity. The basic ionic liquid performs well as a catalyst in the synthesis of methyl oleate from oleic acid and methanol; with a molar ratio of oleic acid to methanol of 1:6 and the amount of catalysts of 15%, the conversion of oleic acid reaches 93.9% after reaction under 60℃ for 10 h. Moreover, the basic ionic liquid synthesized in this work is potential for application in industry, due to its easy recyclability from the reaction system as well as the green and reusable nature.