The corrosion behaviour of ionic liquid 1-butyl-3-methylimidazolium tetrachloroferrate (C 4 C 1 imFeCl 4 ) towards A36 mild steel was studied through experiments and quantum calculations. The corrosion rates were obtained through immersion tests both in open and controlled environments. The surface morphology of the A36 mild steel was investigated using scanning electron microscopy (SEM). The effects of temperature and water content on the corrosion of the ionic liquid towards A36 mild steel were studied through electrochemical corrosion measurement techniques. The results show that the corrosion of C 4 C 1 imFeCl 4 towards the mild steel in the open environment is 17 times higher than in the control environment. The corrosion rate increases with increasing temperature and water content in C 4 C 1 imFeCl 4 . Density Functional Theory (DFT) calculations were performed to gain some insight into the interactions of C 4 C 1 imFeCl 4 with the A36 mild steels surface. © 2016 Elsevier B.V. All rights reserved.