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Utilization of mangosteen rind extract as carbon steel inhibitors in the environment of hydrochloric acid (HCl) 0.1M, 0.5M, and 1.0M. Extracts were carried out by extraction using ethanol solvent at a temperature of 600C with a time of 80 minutes. The research objective was to determine the effect of extract concentration on the carbon steel corrosion rate and its inhibitory efficiency, the effect of the corroding time on the corrosion rate and the inhibitory efficiency for 1000 ppm extract, and study the process of corrosion inhibition on carbon steel in HCl solution. Extract of mangosteen peel extracted using ethanol solvent was applied to HCl solution with a variation of the concentration of extract (100 ppm to 1000 ppm in 3 days, the effect of time of corroding the carbon steel with the addition of 1000 ppm extract. Corrosion rate is calculated based on the difference in weight and corrosion products shown by microscope optics The results of the extraction process research carried out at 600C with 80 minutes with a stirring of 700 rpm produced a yield of 16.71% with a ratio of mangosteen peel powder and 1: 11. The inhibitory properties of mangosteen peel extract for three (3) days increased with increasing extract concentrations up to 76.53% in 0.1M HCl solution and 28.83% in 1.0M HCl solutions. For the addition of 1000 ppm mangosteen peel extract showed inhibitor efficiency reached about 90% at 2 days of corrosive time in HCl 0 , 5 M, 87% in 1.0 M HCl solution, and 81% in 0.1 M HCl solution. Mechanism of mangosteen peel extract performance agai carbon steel corrosion inhibitors through the process of diffusion of compounds in extracts on the surface of carbon steel and react with ferro ions (Fe 2 +) to form chemical covalent coordination coordinate the surface of carbon steel with a thickness of 76 µm.