The pure yttrium orthovanadate crystal has been widely used in polarizing optics such as beam splitters, prism polarizers and optical isolators. The measurement of the nonlinear refractive index is an important method for the study of the nonlinear optical quality and investigation of optical inherent damages in crystal. We have measured the nonlinear refractive indexes of a YVO4 crystal along the orientations of ［100］ and ［001］ by the “Z-scan” method, and found that the nonlinear refractive indexes are generally equal but opposite.