Benzimidazoles are veterinary drugs widely used for prevention and treatment of parasitic infections in agriculture and aquaculture. The benzimidazoles are a large chemical family used as antimicrobial agents against the wide spectrum of microorganisms [1-10]. In this study Henry’s law constants at T = 293.2K are calculated for some Benzimidazole and derivatives drugs in water by density functional theory (DFT) methods at B3LYP (6-31+G**) levels of theory using the Poisson-Boltzmann solvation model.