Enzymes have been extensively used in many industries for the last 20 years. They are becoming more common because of new areas of application. The limitations of applications of enzymes are activity, specificity, stability, and price. Higher enzyme activities and less susceptibility of process conditions are desirable. Therefore, in some cases, purified enzyme extracts are needed. The purpose of this study is the isolation and purification of diamine oxidase (DAO) of pea seedlings and pig liver. The relationship between pea seedlings growth rate and enzyme activity is established. DAO of pea seedlings and pig liver is prepared by way of tissue disruption with homogenization, centrifugation, fractionation with ammonium sulfate, precipitation of inert components, column electrophoresis, and DEAE-cellulose column chromatography. The specific activity of disrupted pea seedlings cells was measured as 0.017 (U/mg protein), and the pig liver DAO activity was measured as 0.00037 (U/mg protein). The specific enzyme activity from pea seedlings was increased to 6.750 (U/mg protein). On the other hand, the specific enzyme activity from pig liver was increased to 0.30 (U/mg protein). The final enzyme extract from pea is 400-fold purer than raw material, and the final enzyme extract from pig liver is 820-fold purer than raw material.