The role of d orbitals in the bonding of H~3PO is studied using our developed method of polarized fregment orbital analysis. The whole molecule H~3PO is divided into two fragments H~3P and O. Then the polarized fragment orbitals in molecular environment (FOM) are calculated using 6-31G^* basis set. Whole molecule is recalculated using the FOM basis set in which the d functions are deleted. The optimized P-O bond length is close to the result of RHF/6-31G^*. The results of this study lead to a refined picture of the nature of hypervalence in H~3PO. The role of d functions of phosphorus atom in the wave function of H~3PO is only a polarized function just as p functions are customarily added to hydrogen atom s functions. The "valence d orbital" role should be rejected in molecule H~3PO.

Key words: PHOSPHORUS, CHEMICAL BONDS, MOLECULAR ORBITAL THEORY, AB INITIO CALCULATION, PHORSPHORIC ACID