Oxidative stress could be increased with high-intensity exercise. It is a significant causal factor to dysfunctional immune response. Thus, high-intensity exercise is a risk of immunosuppression. Cashew apple which is a waste product of cashew nut comprises efficient antioxidants such as vitamin C and anacardic acids. Thus, supplementation of juice produced from cashew apple (CAJ) may reduce suppression of immune function. This may prevent post-exercise infection in sport players. The present study aimed to investigate effects of acute ingestion of CAJ on oxidative stress and white blood cells (WBCs) count in healthy trained subjects. This study was randomized crossover design. Ten healthy trained men aged between 16 and 29 years old were enrolled. They randomly ingested either CAJ or placebo (PLA) by 3.5 ml/kg body mass before cycling at 85% of maximal oxygen consumption for 20 min. Blood samples were obtained at rest, 20 min after the ingestion, immediately after the exercise and at 30 min of recovery period to determine oxidative stress and WBCs count. One week later, they received the other research drink and performed similarly to the previous visit. Oxidative stress was determined by plasma vitamin C, malondialdehyde (MDA) and nitric oxide concentrations. WBCs counts were determined by total WBCs, neutrophil, monocyte and lymphocyte counts. Data are expressed as mean ± SD. The differences of variables within and between groups were analyzed by repeated measures ANOVA and Bonferonni. The results show that there were significantly lower plasma MDA concentrations immediately after the exercise (0.83 ± 0.52 vs 1.08 ± 0.65 μmol/L, p<0.05) and during recovery period (0.73 ± 0.18 vs 0.95 ± 0.61 μmol/L, p<0.05) in the CAJ group compared to the PLA group. There was significantly higher plasma vitamin C concentration at 20 min after the ingestion (0.27 ± 0.11 vs 0.16 ± 0.12 μg/mL, p<0.05) in the CAJ group compared to the PLA group. Plasma nitric oxide concentration was not different between PLA and CAJ groups at any time-point. WBCs, neutrophil, monocyte and lymphocyte counts were not changed at any time-point in both PLA and CAJ groups without any difference between groups. In conclusion, acute ingestion of CAJ can decrease oxidative stress by increasing plasma vitamin C and decreasing plasma MDA. However, white blood cells counts were not affected.