The aim of this study was to determine the influence of exercise on activity of erythrocyte superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT) and plasma malondialdehyde (MDA), beta-carotene, retinol levels in adolescents with Down syndrome (DS). Twenty adolescents with DS (14.86 +/- 7.07 years) performed a 12-week training program. Body composition was measured by bioelectric impedance method. SOD, GPx, CAT, MDA, retinol, beta-carotene levels was determined spectrophotometrically. When compared to baseline, MDA level was increased (P<0.05). SOD, GPx activities and beta-carotene level were decreased (P<0.05). There was no difference during pre-post exercise in terms of CAT activity and retinol level (P>0.05). The mean value of percentage of fat mass was reduced. Regular exercise decreased SOD, GPx activities and beta-carotene level and did not affect CAT activity and retinol level in individuals with DS. Exercise increases oxidative stress depending on level of training.