${gamma}-Glutamylamine$ cyclotransferase was purified to homogeneity from soybean (Glycine max) seeds. To our knowledge, it is the first purification of the enzyme from plant origins. The molecular weight of the enzyme estimated by Sephacryl S-300 gel filtration and SDS-PAGE was 27,000, indicating that the enzyme is a monomer. The optimal pH for activity was 8.6. The Km value for ${gamma}-glutamyldansylcadaverine$ was 11 ${mu}M$. The enzymatic activity was substantially inhibited by the addition of p-chloromercuribenzoate and partially inhibited by the $Cu^{2+}$ ion. However, neither other modification reagents nor other divalent metal ions affected the enzymatic activity. The comparison between the enzymatic activities of seed extracts treated with cycloheximide and control extracts, and the detection of the same single protein band by western blot analysis at the dormant stage without inhibition with distilled water indicate that ${gamma}-Glutamylamine$ cyclotransferase is already present at the dormant stage and gradually activated during germination in soybean seeds.