Water extracts of cassava leaves (Manihot esculenta) has been studied as a corrosion inhibitor for steel in sulfuric acid solution. Cassava Leaf Extracts are Soluble in Water (CLESW) is obtained by evaporation. Cassava leaves so that the hot steam flows wither. Cassava leaves are withered squeezed resulting in a water solution. Aqueous solution left for 3 days and then separated between deposition and solution. The solution obtained was concentrated to vaporize. The concentrated extract at a concentration of 0.1% for; 0.5%; 1%; 5%, and 10% and tested on steel as a corrosion inhibitor in sulfuric acid solution. Measurement of steel corrosion rate and corrosion inhibition efficiency with methods of losing weight, electrochemical instrument and the steel surface seen from SEM measurements. Results showed that the cassava leaf extract from soluble in water in sulfuric acid solution can be used as a corrosion inhibitor of steel. Corrosion rate without the use of a cassava leaf extracts corrosion inhibitor are soluble in water is greater than the use of the corrosion inhibitor. The surface of the steel without corrosion inhibitor is more porous than the presence of inhibitor corrosion it. The adsorption mechanism of the CLESW on mild steel in 0,5 M H2SO4 solution was typical of physisorption.