The influence of 2-[3-(2-oxo-2-phenylethylidene)-1,4-dihydroquinoxaline-2(1H)-ylidene]-1-phenylethanone (Qx1) and amino-2-aniline (Diam1) on the corrosion of steel in 1 M HCl solution has been investigated by weight loss measurements, potentiodynamic polarisation and impedance spectroscopy (EIS) methods. The inhibiting action increases with the concentration of Qx1 and Diam1. The highest efficiency (85%) is obtained at the 10-4 M Qx1. There is good agreement between gravimetric and electrochemical methods (potentiodynamic polarisation and EIS). Polarisation measurements also show that Qx1 and Diam1 act as mixed inhibitors. The cathodic curves indicate that the reduction of proton at the steel surface happens with an activating mechanism. Qx1 adsorbs on the steel surface according to Langmuir adsorption model. Effect of temperature is also studied between 308 and 353 K.