The covalency is calculated for several compounds with diamond structure, zinc blend structure and rock salt structure using the DV-Xalpha cluster method. The covalency of noble metal halides is in the border between that of the four-fold coordinated compounds and that of the six-fold coordinated compounds. These calculation results on the covalency support the tendency of the Phillips's ionicity. The obtained covalency is also compared with that estimated from the lattice energy obtained by both the Born-Haber cycle and the Born-Lande equation. (C) 2004 Elsevier B.V. All rights reserved.