Abstract: The ionic liquid \BMIM\\AlCl₄\ was synthesized to upgrade heavy oils. The influences of contents of sulfur and water, reaction temperature, and transition metal salts on upgrading heavy oils were investigated. The experimental results show that a certain amount of sulfur in heavy oils is beneficial to the viscosity reduction. The reduction of viscosity by \BMIM\\AlCl₄\ ionic liquid is better when the water content of heavy oils is less than 10%. The optimum temperature to upgrade the Xinjiang heavy oil with \BMIM\\AlCl₄\ ionic liquid is 65℃~85℃. The combination of transition metal salts and \BMIM\\AlCl₄\ can enhance the viscosity reduction in heavy oils. More than 60% of viscosity can be reduced by treating the heavy oil with the mixture of \BMIM\\AlCl₄\ and NiNaph, and in addition, the asphaltene content can be reduced by 78%.