The effects of carboxymethyl chitosan (CT-50) on removal of nickel and vanadium from pipeline crude oil in the presence of microwaves were investigated. CT-50 was synthesized from chitosan (CTS-50, molecular weight 50 million). CTS-50 and CT-50 were characterized by infrared spectroscopy and scanning electronic microscopy. CT-50 was used to remove nickel and vanadium from pipeline crude oil. The effects of several factors, such as initial temperature, microwave time, microwave power and CT-50 dose on nickel and vanadium removal efficiencies from crude oil were evaluated. The results indicated that removal of nickel and vanadium from crude oil using CT-50 was far more efficient than that using CTS-50 under the same conditions. A reaction temperature of 60 degrees C. a microwave power of 300W. a microwave time of 2 min, and a CT-50 dose of 500 mg/L, the nickel and vanadium removal efficiencies from crude oil reached up to 69.79% and 93.66% respectively. Microwaves were thought to enhance the molecular motion and the stable molecular structure of organic compounds of nickel and vanadium became loose in the high-energy state, and they were adsorbed in CT-50 and reacted with the amino (-NH2) and carboxylic (-COO-) groups in the CT-50 molecule. (C) 2010 Elsevier B.V. All rights reserved.