Peroxidases (PODs) are a group of enzymes that are commonly found in bacteria, fungi, plants and animals and have important uses in the food, pharmaceutical industry and clinical diagnostics. Lactoperoxidase (LPO) enzyme, which is included in peroxidase enzyme class, is found milk, saliva and tears in mammals. With thiocyanate and hydrogen peroxide, it forms one of the body's defense systems against infections. Flavonoid derivatives are abundant in plants and constitute an important part of the diet. These derivatives, which are produced synthetically or naturally, have many pharmacological activities. In this study, the effect of some flavonoid derivatives (5,7-Dihydroxy-2-(3-hydroxy-4-methoxyphenyl)-4H-chromen-4-one (a), 3,5,7- Trihydroxy-2-(3,4,5-trihydroxyphenyl)-4H-chromen-4-one (b), 7-Hydroxy-4'-nitroisoflavone (c), 6- Fluoroflavone (d), 7-Hydroxy-3-(4-methoxyphenyl)-4H-chromen-4-one (e), 7-Methoxy-2-phenyl- 4H-chromen-4-one (f)) on the lactoperoxidase enzyme was investigated. Firstly, by using Sepharose- 4B-L-tyrosine-sulfanilamide affinity chromatography, the LPO enzyme was purified 65 fold (with a yield of 23%) from bovine milk and kinetic studies were carried out with flavonoid derivatives using this enzyme. The Ki values of six molecules were found in ranging from 7.85 µM to 0.023 μM. 6- Fluoroflavone was the most effective inhibitor with Ki value of 0.023 μM.