Abstract: The nonrclativistic Xa calculations were carried out in order to obtain the numerical atomic orbitals and orbital electronegativities of the lanthanoid ions in different electronic configurations. The single and double ζ exponents of Slater type basis functions of the atomic orbitals were then obtained by numerical fitting. The effect of charge and electronic configuration of the lanthanoid ions on the orbital exponent and electronegativity is studied and the regression formulas in higher precision are given. These fomulas not only show how the natures of the atomic orbitals vary with the ionic configuration but also provide the basic parameters for studies on the electronic structure of lanthanoid compounds and the iteration formulas for calculations through the self-consistence of charge approach.

Key words: Lanthanoids, Orbital exponents, Orbital electronegativity