We Proposed a simple and an effective method to predict the site occupancy and threshold concentration of metal Ions in lithium niobate. (LiNbO3, LN) single crystal: The ionic energy parameter E defined by the ionic electronegativity and ionic radius, was proposed to describe the electrostatic and "size effects of cations on the structural stability of LN. The dopant location can be easily identified by comparing the E-i deviation of dopant from those of host cations Li+ and Nb5+, and the dopant prefers to occupy the lattice. site With the smaller deviation of E-i. Our calculated occupancies agree Well with those experiniental results, 3 which demonstrate the predictive power, of our present method We in this : 2 work predicted the preferred occupancies of 60 metal ions in LN single crystal. Further, the threshold concentrations of some frequently used dopants were calculated on the basis of the assumption that all doped LN crystals can endure tire same variation Of E-i.