PurposeThe purpose of this paper is to investigate the inhibition effect of 2‐aminoethane thiol hydrochloride, 2‐cystamine dihydrochloride, 2,3‐dimercapto‐1‐propanol, 1,2‐ethanedithiol, and the synergistic effect of these compounds with halide ions (Cl−, Br−, I−) and with some metal cations (Co2 + , Ni2 + , Cu2 + , Zn2 + ).Design/methodology/approachThe inhibiting effect of the studied thiols on the corrosion of carbon steel in 0.5 M H2SO4 solution were investigated using potentiodynamic polarisation, electrochemical impedance spectroscopy and linear polarisation methods.FindingsThe inhibition action of thiols depends mainly on the type of the heteroatom present in the inhibitor molecule. The increase in inhibition efficiencies with increase in inhibitor concentration revealed that the studied compounds were adsorbed onto steel surfaces and the adsorption mechanism obeyed the Langmuir adsorption isotherm. Polarisation curves indicated that thiols containing both N and S atoms in their structure behaved as mixed type inhibitors, while thiols containing only an S atom in their structure acted essentially as anodic inhibitors. The increase in the inhibition efficiencies of thiols with the addition of halide ions indicates that halides play important role in the adsorption process. The synergistic effect of the studied metal cations could be explained by the adsorption of complex ions formed from thiol molecules and metal cations.Originality/valueThis paper provides useful information about the relationship between inhibition efficiencies and the structures of thiols and clarifies the mechanism of the synergistic effects of some halides and some metal cations.