The accelerating effect of sunlight on the rancidity of soybean oil and the efficacies of several anti-oxidants were measured. The result is as follows: 1. The ac야 value and peroxide value of soybean oil were 0.16 and 1, 72 respectively. 2. the peroxide value of soybean oil which was exposed to sunlight nine hours a day for six days was 134.3: 21 times of that which was not exposed to sunlight. 3. The peroxide value of the soybean oil with 0.02~0.06% BHA decreased a little, but not significantly. 4. The anti-rancidity effect of BHT was a little stronger than BHA. 5. The anti-rancidity effect of ascorbic acid alone was negligible. 6 The peroxide value of soybean oil with an anti-oxidant which comprised ascorbic acid, BHA and BHT decreased to one third of that which was not treated with anti-oxidant.