Thiourea and its derivatives have been studied for several decades for their corrosion inhibition characteristics with steels. However their interaction mechanisms with steel are not well understood. Such an understanding may be vital for design of novel thiourea derivatives as corrosion inhibitors for steels. We have carried out state-of-the-art density functional theory (DFT) computations and experiments (weightloss polarization and electrochemical impedance) to understand the effect of thioureas on corrosion of steel. The interactions of several thiourea derivatives viz. thiourea dibutyl thiourea acetyl thiourea diphenyl thiourea tetramethyl thiourea and ethylene thiourea have been investigated. DFT indicates strong interactions between Fe atoms of the surface and C S - atoms of the molecule while the N-atoms do not show any significant proclivity towards interactions with the Fe-surface. Among the hollow on-top and bridge sites on the Fe-surface S-atom was found to preferentially occupy the bridge site which facilitates formation of two strong Fe-S bonds which possibly explains the strong corrosion inhibition by thioureas on steels. Besides DFT computations provided insights for design of much more promising molecules for corrosion inhibition. Experimentally dibutyl thiourea was found to have an extraordinary inhibition effect for steel in 1N HCl in accordance with DFT computations.Keywords: Corrosion inhibitors thiourea derivatives DFT experiments