The influence of thiophene and five of its substituted derivatives on the corrosion inhibition of steel in 0.5 M H2SO4 solution was studied using weight-loss, electrochemical polarisation, and impedance measurements. 5-tert-butoxythiophene-2-carbaldehyde phenylhydrazone (TBCP) is the best inhibitor and its inhibition efficiency increases with increase in concentration to attain 87% at 5x10(-3) M. Potentiodynamic polarisation studies clearly reveal that it acts essentially as a cathodic inhibitor. The partial eta-charge on atoms has been calculated. A correlation between the highest occupied molecular orbital E (HOMO) and inhibition efficiencies was sought. The inhibition efficiency of TBCP is not affected by rise in temperature in the range 298-353 K. E% values obtained from weight-loss and electrochemical methods were in good agreement. Adsorption of TBCP on steel has an S-shaped adsorption isotherm.