Three types of rancidity of coconut oil were studied; hydrolytic one by adding enzyme lipase, ketonic one by adding rotten coconut meat and the last one, oxidative, by adding oxygen in Rancimat apparatus. Free fatty acid,ketone contents and induction time and complete oxidation time were measured as the results of hydrolytic, ketonic and oxidative rancidity, respectively. Rancidity odor of the first 2 types was very repulsive and dependent on the concentration of free fatty acid and ketone. The odor of the oxidative one was mild. The oxidative stability of coconut oil was 4.8 times of rice bran oil. Major rancidities occurred in coconut oil were believed to be the hydrolytic and ketonic types. The lowest concentrations of free fatty acid and ketone that 50 untrained panel could detect were 0.26 % and 0.082 mg./g. Over 60 % of the panelists did not accept the rancidity odors.