Inhibition effect of hexa propylene glycol cyclotriphosphazene (HPGCP) was studied on carbon steel corrosion in 1 M HCl has been investigated in a temperature ranging from 298 to 328 K using weight loss measurements. The inhibition efficiency of HPGCP decreases with the rise of temperature. The values of equilibrium constant (Kads) and adsorption free energy were discussed. The adsorption of inhibitor on metal followed Langmuir’s adsorption isotherm. The thermodynamic parameters of adsorption reveal that there is a strong interaction between inhibitor and carbon steel. The highest inhibition efficiency was observed 10-5 M of HPGCP concentration at different temperature.