An ionic liquid (IL), 1-butyl-3-methylimidazolium perchlorate, [BMIM][ClO4], is synthesized and used as a reducing agent to upgrade a selected heavy oil. The effects of [BMIM][ClO4] on viscosity, density, SARA contents, elemental compositions, and molecular weight of the heavy oil are studied. The results show that the heavy oil treated with [BMIM][ClO4] has reduction in viscosity and density. The results also indicate that the presence of [BMIM][ClO4] significantly changes the composition of the heavy oil. Moreover, the effects of [BMIM][ClO4] on the interfacial tension (IFT) of oil-water and oil recovery are tested. Results shows that [BMIM][ClO4] can improve the mobility of heavy oil by reducing the IFT of oil-water and increase the recovery factor by 79.94%.