Two water soluble acryl terpolymers containing polyvinyl alcohol, acrylamide/acrylic acid and vinyl sulphonic acid (VSA) were synthesized by free radical polymerization in aqueous medium. The morphological structure of the polymers were analysed using FTIR and H-1 NMR, while the thermal properties were analysed by TGA and DSC. The inhibitive action of the terpolymers on corrosion of mid-steel in 1 mol.L-1 HCl was studied using gravimetric, potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) at 303 K. Both the polymers provided inhibition efficiency around 90% which clearly demonstrate that the grafted polymers have effective corrosion inhibiting ability on MS corrosion. (C) 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.