Catalase (EC 220.127.116.11) enzyme is an endogenous antioxidant protein that is found in the cells of many living tissues. It catalyses the conversion of two molecules of hydrogen peroxide into two water molecules and one molecule of oxygen gas without free radicals production. The reaction as follows 2H2O2 ----> 2H2O + O2 Catalase has a high turnover number which means that it can bind to millions of hydrogen peroxide and convert it into water and oxygen per unit second. Catalase is composed of four identical subunits (polypeptide chains) (220,000 to 350,000 kD), each of which contains a heme active site to accelerate bind and decomposition of hydrogen peroxide to water and oxygen. The optimum PH for catalase is 7 and the optimum temperature 37 °C .The cofactors of catalase are heme and NADP. The enzyme is present in liver, kidney and erythrocytes with the highest activity and with the lowest activity in connective tissues .Catalase present in the peroxisomes of nearly all aerobic cells. The enzyme catalase shows a high activity in neuromuscular, cardiovascular and metabolic diseases while shows a low activity in psychiatric and otorhinopharyngologic diseases.Hypocatalasemia, also called acatalasia is a rare autosomal recessive disorder resulting from the absence of catalase enzyme activity.Catalase deficiency increase the risk of diabetes mellitus type 2 due to the damage of pancreatic β-cells which inhibit protein signaling by the effect of H2O2 that come from normal cellular respiration. The technique of analysis was the titration by KMNO4 to detect the amount of H2O2 remained after the decomposition by the effect of catalase the reaction was stopped and started by the change in ph by adding H2SO4 to make the medium acidic and the stop the catalase effect. After titration to the H2O2 the smaller the endpoint the more decomposition to the hydrogen peroxide.