Elevated plasma homocysteine is an independent risk factor for the development of cardiovascular disease. Exercise is generally believed to reduce the plasma homocysteine levels and therefore, being beneficial for cardiovascular disease (CVD). However, there is a possibility that athletes undergoing strenuous training and competition which increase oxidative stress may suffer from increased plasma homocysteine levels. The purpose of this study was to investigate the influence of endurance training on the plasma concentrations of B vitamins and homocysteine in 23 male adolescent field hockey players. Data collection and blood sampling was performed during the training period and non-training period. Following the training period, significant changes in energy and vitamin B6 intakes were observed in these subjects. Plasma vitamin B2, pyridoxal phosphate (PLP) and homocysteine levels were significantly higher during the training period than non-training period, whereas no difference was observed in plasma folate and vitamin B12 levels. Positive correlation was observed between plasma folate and folic acid intakes. When energy, B vitamin intakes were adjusted there was a significant negative correlation between plasma homocysteine levels and plasma riboflavin, folate and vitamin B12 levels. In conclusion, it is suggested that athletes with oxidative stress by strenuous exercise may need B vitamins since riboflavin, folic acid and vitamin Bl2 were shown to be negatively correlated with plasma homocysteine in athletes during the training period