The benzimidazole nucleus is an important heterocyclic ring, and interest in the chemistry,synthesis and microbiology of this pharmacophore continues to be fuelled by its antifungal [1],antitubercular [2], antioxidant [3, 4], and antiallergic [5, 6] properties. In this study Henry’s law constants at T = 293.2K are calculated for some Benzimidazole and derivatives drugs in water by Hartree Fock methods at (HF/6-31+G** ) level of theory using the Poisson-Boltzmann solvation model.