The inhibitor effect of two isomers namely 2-(1',5,5'-trimethyl-1H,1'H-3,3'-bipyrazol-l-yl)ethanol (I-TBE) and 2-(1',5.5'-trimethyl-1H,2'H-3,3'-bipyrazol-2-yl)ethanol (2-TBE) on the corrosion of mild steel in 1.0 M hydrochloric acid has been investigated at 308 K using weight loss measurements and electrochemical techniques (impedance spectroscopy and polarisation curves). Inhibition efficiency is dependent upon the pyrazole structure. with I-TBE serving as a better inhibitor than 2-TBE and its inhibition efficiency increases with the increase of concentration of inhibitor to attain 93% in the presence of 10(-3)M. Polarisation curves indicate that I-TBE and 2-TBE act essentially as cathodic inhibitors. Efficiency (E) percent values obtained by various methods are reasonably good in agreement. EIS measurements show an increase of the transfer resistance with the inhibitor concentration. The temperature effect on the corrosion behaviour of steel in 1.0 M HCl without and with the inhibitor at 10(-3)M is studied in the temperature range 308-333 K. Some thermodynamic parameters such as adsorption heat (Delta H degrees). adsorption entropy (Delta S degrees) and adsorption free energy (Delta G degrees) have been calculated by employing thermodynamic equations. Kinetic parameters such as apparent activation energy and pre-exponential factor have also been calculated. Adsorption of I-TBE on the mild steel surface in 1.0 M HCl follows the Langmuir isotherm model.