Corrosion is an unavoidable but a controllable proc ess. Due to the issues of toxicity of substances, t here is an increasing interest in exploration and utilization of eco-friendly inhibitors, which are also known as green inhibitors. The inhibitive effects of aqueous extra cts of Opuntia ficus indica (OFI) on the corrosion of mild steel, in hydrochloric acid have been investigated by weight loss and polarisation measurements. Weight loss mea surements gave an inhibition efficiency of about 91 % in the presence of 5g/l at 308K. EIS results revealed that green inhibitor effects excellently as a corrosion inhibitor for C3 8 steel in 1 M hydrochloric acid media with retarde d the dissolution reactions to an extent dependent on the metal used. Polarisation measurements indicate tha t all the extracts increase the polarisation of the cathodic reaction of all the steel tested and the anodic pol arisation, have no effect on the anodic reaction. The above results sh owed that OFI acted as a mixed-type corrosion inhib itor and the mechanism of inhibition has been discussed. The cha nges in impedance parameters (charge transfer resis tance, R ct , and double layer capacitance, C dl ) were indicative of adsorption of OFI on the steel surface, leading to the formation of protective films. The adsorption of us ed compound on the steel surface obeys Langmuir’s i sotherm. The apparent activation energy, enthalpy of the dissolu tion process and the free energy were determined an d discussed