The effect of free fatty acid(FFA) on the oxidative stability of DHA oil produced by Schizochytrium sp.Was studied.The oxidation of purified DHA oils added with three kinds of FFA were monitored by measuring peroxide value(POV,index of primary oxidation products) and thiobarbituric acid reactive substances(TBARS,index of secondary oxidation products) under Schaal oven test condition.Results showed that the oxidative stability of purified DHA oils was decreased by adding FFA.With the control of alkane,the pro-oxidant effect of FFA due to its carboxyl groups was initially confirmed.