Mild steel is widely used in fabrication of reaction vessels, storage tanks, petroleum refineries, and so on, but it is severely attacked in acid solutions. Despite continuing advances in development of corrosion-resistant materials, the use of chemical inhibitors often remains the most practical and cost-effective means of preventing corrosion. Organic compounds containing nitrogen, sulphur, oxygen, and heterocyclic compounds with a polar functional group and a conjugated double bond have been reported to inhibit mild steel corrosion. There are a wide range of organic inhibitors but unfortunately most of them are expensive and health hazardous. Thus, it remains an important goal to find low cost and eco-friendly inhibitors. Few non-toxic compounds belonging to pharmaceutically active compound group have been investigated for their corrosion inhibition properties for mild steel in acid media. Plant extracts are rich sources of environmentally acceptable corrosion inhibitors. The plant extracts non- toxic and readily available. These extracts contain many organic compounds which have polar atoms such as O, N, P and S. They are adsorbed onto the metal surface through these polar atoms; protective films are formed. Adsorptions of these ingredients obey various adsorption isotherms for example Langmuir adsorption isotherm and Temkin isotherm. In present work we have reviewed structural feature of few green corrosion inhibitors and their mechanism of corrosion inhibition by analysing data from weight loss measurements, tafel polarization and EIS investigations.