CORROSION inhibition of API X120 steel in a 1M sulfuric acid solution at altered temperatures was investigated utilizing a new eco-friendly surfactant (Caprylamidopropyl Betaine (CAPB)) by Gravimetric and electrochemical test (containing potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS). Surface characterization tests containing scanning electron microscopy (SEM), and atomic force microscopy (AFM) are utilized in the study. In addition, kinetic and thermodynamic parameters were measured and discussed. The overall results displayed that the corrosion rate of API X120 steel was significantly lowered with improving the temperature. The polarization curves lead to the CAPB inhibitor is influenced both anodic and cathodic reactions (mixed type inhibitor). Analyses of the surface topography designated an appreciable decrease in the surface roughness as the dose of the inhibitor in the solution improved. Energy-dispersive X-ray and X-ray photoelectron spectroscopy revealed the presence of adsorbed nitrogen atoms on the API X 120 steel surfaces. This work provides a promising eco-friendly inhibitor for mitigating the corrosion of API X120 steel in highly acidic brine environments.