The inhibiting effect of two organic copolymers namely poly(vinyl caprolactone-co-vinyl pyridine) (PVCVP) and poly(vinyl imidazol-co-vinyl pyridine) (PVIVP) on the corrosion of steel in phosphoric acid was investigated at various temperatures. The study was carried out by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and weight loss measurements. Inhibition efficiency (E %) increased with polymer concentration to attain 85% at 10(-4) M for PVIVP. Adsorption of polymers on the steel surface in 2 M H3PO4 followed the Langmuir isotherm model. EIS measurements show that the dissolution of steel occurs under activation control. Polarisation curves indicate that the tested polymers functioned as cathodic inhibitors. E % values obtained from various methods used are in good agreement with each other. The temperature effect on the corrosion behaviour of steel in 2 M H3PO4 in the presence and absence of the inhibitor was studied in the temperature range 298-338 K. The adsorption free energy (Delta G degrees (ads)) and the activation parameters (E-a, Delta H degrees(a), Delta S degrees(a)) for the steel dissolution reaction in the presence of polymer were determined.