The aim of this study is to determine the antioxidant properties of kefir samples produced from different cow/soy milk mixtures. Antioxidative activities such as the inhibition of ascorbate autoxidation, reducing activity, the scavenging effect of superoxide anion radicals and hydrogen peroxide of kefir samples were determined. Kefirs produced from whole soymilk had the highest inhibition rate of ascorbate autoxidation. Reducing activities of kefir samples, expressed as equivalent amounts of cysteine, were found statistically different and elevated by increased soymilk ratio. Results of the inhibition of superoxide radical generation of cow, cow/soy and soymilk kefir samples were found statistically different. However, the effect of fermentation on this activity neither with kefir grain nor culture was significant. Results indicated that none of kefir samples exhibit a hydrogen peroxide scavenging activity.