Density functional theory (DFT) calculations and atomistic Monte Carlo simulations were performed on hexahydro-1,3,5-triphenyl-s-triazine (Inh1), hexahydro-1,3,5-p-tolyl-s-triazine (Inh2), hexahydro-1,3,5-p-methoxyphenyl-s-triazine (Inh3), hexahydro-1,3,5-p-aminophenyl-s-triazine (Inh4), hexahydro-1,3,5-p-nitrophenyl-s-triazine (Inh5) molecules in order to study their reactivity and adsorption behaviour towards steel corrosion. DFT results indicate that the active sites of the molecules were mainly located on the N atoms of the triazine ring and on the aromatic rings containing substituted polar groups. Monte Carlo simulations were applied to search for the most stable configuration for the adsorption of the inhibitor molecules on Fe(110) surface both in vacuum and in aqueous solution. The investigated molecules exhibited strong interactions with iron surface. In aqueous solution all the investigated molecules displaced water molecules and were strongly attracted to the Fe surface as evident in their large negative adsorption energies compared to that in vacuum. The DFT reactivity indicators as well as the adsorption strength from the outputs of Monte Carlo simulations of the studied molecules on Fe(110) surface in vacuum and in the presence of water follow the trend: Inh4 > Inh3 > Inh2 > Inh1 > Inh5. The theoretical data obtained are in good agreement with the experimental inhibition efficiency results earlier reported.