The invention relates to a use of a stem cell conditioned medium to inhibit oxidation for anti-aging skin. First, mesenchymal stem cells are cultured in a cell culture dish containing complete growth media. After mesenchymal stem cells are sub-cultured in the basal media for three times, a conditioned medium can be acquired from the basal media. Accordingly, cosmetics containing at least 10 wt.% conditioned medium can effectively scavenge free radicals and increase the survival rate of skin cells under oxidative stress so as to achieve efficacy of anti-aging skin.
