Abstract: The fators affecting the lipase activity and the acid value of oil in walnut under different storage conditions were studied. The results showed that the lipase activity in walnut were affected significantly by water content and storage temperature, and the acid values of oil were affected significantly by walnut varieties, water content, storage methods and storage temperature. If the lipase activity was high, the acid value rose rapidly. When the acid value was above 7.5, the walnut became rancid seriously and the color and flavor of walnut kernel were deteriorated.