The matrix elements of spin – orbit interaction (SOI) have been evaluated for the ground level 2F7/2 of Yb3+ ions in crystals. The dependence of the normalized ratios of SOI relative to the free ion Yb IV – value on the crystal field strength Nv has been found similar to the nephelauxetic effect. The variations with Nv of the nephelauxetic parameter β, maximum splitting of the ground level, and the number of crystal – field parameters have been discussed. The analysis comprises 49 symmetry sites of Yb3+ ions in stoichiometric or doped compounds: complexes with inorganic ligands, simple and complex oxides, halogenides, and semiconductors. A discrepancy has been found between theoretical and experimental values of the maximum splitting in the ground level 2F7/2 of Yb3+ ions in crystals.