Most crude oils contain traces of metal complexes, among which vanadium (V) and nickel (Ni) compounds are the most harmful poisons to the catalysts of fluid catalytic cracking (FCC) and hydrogenation units. These metals are proven to be extremely hard to remove, since they exist in crude oil as stable oil-soluble complexes. The microwave technology provides a new way for Ni/V removal, their removal efficiency using chemical reagents and the mechanism of microwave-assisted demetallization were studied in this paper. It was concluded that the demetallization efficiency can be highly enhanced under microwave irradiation. There is no specific structural selectivity for vanadium porphyrins during microwave treatment process. The demetallization agent methanesulfonic acid, containing a sulfonyl acid group was found to react with VO2+ and Ni2+. Ni and V were removed from porphyrin ring without destroying the ring structure, corresponding water soluble inorganic salts were formed, thus can be successfully separated from crude oil by washing or desalting process. (C) 2015 Elsevier B.V. All rights reserved.