A form of lipoxygenase (EC 1. 13. 11. 12) was isolated from rice brans which were obtained from the milling of rice caryopsis, and was purified partially but to give an electrophoretically homogeneous form. The molecular weight of the enzyme was found to be about 100, 000 daltons based on the gel filtration experiment. The optimum activity for the catalytic hydroperoxidation by rice bran lipoxygenase was obtained at neutural pH (pH 6. 8 to 7. 0) and at 30℃. The enzyme show ed a relative stability under the neutral pH and at room temperature, but a marked deactivation of the enzyme protein was observed at the preincubation temperature abov a 50℃. The first order deactivation constants for the enzyme were calculated to be 0.002, 4.014, 0.136 and 0.281 per minute at 40, 50, 60 and 70℃, respectively. The isoelectric point of the enzyme was about 4. 8 based on the isoelectrofocusing experiment, The enzyme was found to be very specific toward linoleate for the hydroperoxidation as in the case of the soybean enzyme, but the estimated K_m values for linoleate and molecular oxygen were found to be about the same. Based on the steady state kinetic experiment measuring the initial velocity of the enzyme reaction, it was also suggested that the hydroperoxidation of linoleate is proceeded through the formation of a ternary complex between the enzyme and two substrate ligands.