Demetallization of high-viscosity crude oil from the Liaohe oil field has been investigated by means of a SH-I electric desalting instrument. The high-viscosity crude oil which is similar to residual fractions of ordinary crude oil of both high-density and high-viscosity belongs to low-sulfur naphthenic crude oil, since it contains various metallic elements with calcium of 406.98 mu g/g as the highest concentration, the rest being nickel, iron, sodium, manganese, etc. Research results demonstrate that under the proper conditions the demetallization agents MPTE, MPTF, and their mixtures could reduce the concentration of almost all metallic elements, e. g., calcium, iron, and manganese, in crude oil effectively. Moreover, the demetallization agents developed in this work are environmentally friendly because they contain no heteroatoms of P or S. Meanwhile, the important factors which may affect demetallization efficiency, such as the viscosity of the crude oil, the type and dosage of the demetallization agents, the acidity of their aqueous solution, etc., have been determined experimentally.