 This study investigated the use of expired ampicillin as a mild steel corrosion inhibitor in an acidic environment. The results showed that the drug had a high inhibition efficiency of over 95% increasing the charge transfer resistance at the steel solution interface. It also reduced the corrosion current density and acted as a mixed type corrosion inhibitor. Ampicillin was found to be physically and chemically adsorbed onto the steel surface, which was confirmed by SEMEDS analysis. This article was offered by Cunadayya Lamri, Ajahar Khan, Jeenat Aslam, and others.