A theoretical study on the chromium (Cr) doping effect on the crystal structure of metallic VO2 has been performed by first principles calculation based on local density approximation (LDA). The results are consistent with the experimental observations: the substitution impurity of Cr on cation site (Cr-v) defects are created by Cr-doping and the Cr-doping results in the shrink of the volume in the crystal unit cell. The substitution of Cr gives rise to two different V-V distances and charge transfer from V to Cr. (C) 2004 Elsevier B.V. All rights reserved.