Peroxidases are extensively found in plants, microorganisms and animals and are resourceful biocatalysts with a wide number of applications in biomedicine as well as biotechnology. The enzyme peroxidase was isolated from the leaves of Brassica oleracea using 0.2 M phosphate buffer at pH 7.0. Different dilutions of this crude enzyme were then examined for peroxidase activity assay. The substrate 4-aminoantipyrine-phenol was used to determine peroxidase activity. The effect of enzyme concentration, substrate concentration as well as temperature and pH on enzyme activity was then determined. The kinetic constants Km and Vmax were also determined. Based on Lineweaver-Burk plot with substrate concentration in the range of 4.25 x 10-4 M to 16.15 x 10-4 M the Km was found to be 7.14 mM and Vmax was found to be 0.1 mole/min. The optimum temperature was 50°C and the optimum pH was 8.0 for the peroxidase enzyme. These optimum conditions were used to determine enzyme activities in the cabbage sample.