The aim of this study was to determine the influence of long-term docosahexaenoic acid (DHA) dietary supplementation on the erythrocyte fatty acid profile and oxidative balance in soccer players after training and acute exercise. Fifteen volunteer male athletes (age 20.0 ± 0.5 years) were randomly assigned to a placebo group that consumed an almond-based beverage (n = 6), or to an experimental group that consumed the same beverage enriched with DHA (n = 9) for 8 weeks. Blood samples were taken in resting conditions at the beginning and after 8 weeks of nutritional intervention and training in resting and in post-exercise conditions. Oxidative damage markers (malonyldialdehyde, carbonyl and nitrotyrosine indexes) and the activity and protein level of antioxidant enzymes (catalase, superoxide dismutase, glutathione reductase and peroxidase) were assessed. The results showed that training increased antioxidant enzyme activities in erythrocytes. The experimental beverage increased DHA from 34.0 ± 3.6 to 43.0 ± 3.6 nmol/10(9) erythrocytes. DHA supplementation increased the catalytic activity of superoxide dismutase from 1.48 ± 0.40 to 10.5 ± 0.35 pkat/10(9) erythrocytes, and brought about a reduction in peroxidative damage induced by training or exercise. In conclusion, dietary supplementation with DHA changed the erythrocyte membrane composition, provided antioxidant defense and reduced protein peroxidative damage in the red blood cells of professional athletes after an 8-week training season and acute exercise.