The inhibitory effect of a new derivative of the indazole family, namely, (Z)-2-(1-methyl-5-nitro-1H-indazol-4-yl)-3-(3-nitrophenyl) acrylonitrile (51K2) against corrosion of carbon steel in 1 M HCl medium at a temperature of 25°C has been evaluated by different techniques such as gravimetric methods, potential-intensity curves, and electrochemical impedance spectroscopy. The impact of the concentration on the inhibition efficiency was also studied. The results of weight loss measurements and electrochemical analyses obtained showed that the addition of 51K2 increases the inhibition efficiency by decreasing the corrosion rate, with a maximum inhibitory efficacy of 80%. In other words, 51K2 is a good anodic-type corrosion inhibitor of carbon steel in 1 M HCl.