Lipoxygenase (linoleate:oxygen oxidoreductase; EC 1.13.11.12; LOX) is a key enzyme in the signaling pathway leading to the production of biologically active compounds involved in plant growth development and stress responses. In this study the novel LOX enzyme from opium poppy (Papaver somniferum L.) seedlings was purified to electrophoretic homogeneity and characterized. LOX activity during the germination of opium poppy seeds was analyzed, and the highest LOX activity was determined on the fourth day of germination. Opium poppy LOX was purified from 4-day-old poppy seedlings after ammonium sulfate precipitation followed by hydrophobic chromatography (Phenyl-Sepharose CL-4B), ion exchange chromatography (Q-Sepharose), and affinity chromatography (linoleyl-aminopropyl agarose) for the first time. The relative molecular weight of purified LOX was estimated to be 78 kDa by immunoblotting. The highest enzyme activity occurred at pH 6.5 and 0.75 mM calcium ion concentration. LOX showed preferential activity towards linoleic acid followed by linolenic acid as a substrate. To investigate the positional specificity of the LOX reaction, purified LOX was incubated with linoleic acid, and the products were analyzed by high-performance liquid chromatography. Opium poppy LOX converted linoleic acid to 13-hydroperoxy-(9Z,11E)-octadecadienoic acid (63.5%) and, to a lesser extent, 9-hydroperoxy-(10E,12Z)-octadecadienoic acid (36.5%).