10.22376/ijpbs.2019.10.1.p1-12 Volume 4 Issue 1 2013 (January - March) In the present study, a sensitive modification of the colorimetric assay for catalase activity is reported. This assay is based on the reaction of undecomposed hydrogen peroxide with ammonium molybdate to give a yellowish color, which has maximum absorbance at 354 nm. Catalase-like activity is calculated from a comparison with the activity of a certified standard enzyme with known unit activity (50 k.units/litre). The seminal plasma catalase activity of a sample of normal individual has been determined. The imprecision of the method was calculated by measuring the coefficient of variation, which equals to 2.61% within a run and 5.35% between run. The catalase assay performed using kinetic method yielded a good correlation (r = 0.98504). MAHMOUD HUSSEIN HADWAN, LAMIA A. ALMASHHEDY AND ABDUL RAZZAQ S. ALSALMAN. catalase-like activity; hydrogen peroxide; seminal plasma; ammonium molybdate. 949-954