Oxidative stabilities of fat in DHA(cis-4,7,10,13,16,19-docosahexaenoic acid)-added dry milk and ordinary dry milk during storage were studied by determining thiobarbituric acid values of samples. Two kinds of milk powder samples were purchased in the local supermarket and $2{pm}0.05;g$ of samples were transferred into serum bottles, which were stored under the light or under dark The oxidation of fat in DHA-added milk powder was higher than that of fat in ordinary milk powder and the acceleration was more evident in the presence of light Light and unsaturated fats accelerated synergistically oxidation of milk fat Addition of DABCO(diazabicyclooctane), which is an efficient singlet oxygen quencher, significantly decreased the photooxidation of milk fat This result clearly suggested that singlet oxygen oxidation (Type II reaction) was involved in the system. Deceleration of milk fat oxidation by DABCO was higher in the DHA-added milk powder.