Lipoxygenase (LOX), one of the main oxidative catalysts in plants, is involved in the regulation of growth and senescence. We investigated changes in LOX activity or its properties as they related to the development of oat plants at four stages (germination, growth, natural senescence, and dark-incubated senescence). LOX activity was high during early growth and at senescence. At pH 4.5, activity showed an abrupt surge compared with a normal enzyme reaction pattern at pH 6.5. The optimum reaction temperature was $25^{circ}C$ ; LOX and peroxidase exhibited similar activity patterns. Polyacrylamide gel electrophoresis revealed that the purified LOX consisted of three isoenzymes in germinating seeds, two in growing seedlings, and three during both natural and dark-induced senescence. As determined by isoelectric focusing, the isoelectric points (pI) of LOX ranged from 3.6 to 6.5 throughout the four developmental stages; for natural or dark-induced senescence, the pi was 9.0.