Smoking is well known to be associated with increased indices of tree radical-mediated damage of DNA, indicating that smoking may exacerbate the initiation and propagation of oxidative stresses, which are potential underlying processes in the pathogenesis of many diseases. The purpose of this study was to evaluate whether a daily regimen of green vegetable drink supplementation to smokers can be protective against endogenous lymphocytic DNA damage and whether it could enhance other antioxidant status. Twenty nonsmokers and nineteen smokers aged 23-60 were given 240 ml of green vegetable drink every day for 8 weeks in addition to their normal diet, and blood samples were drawn before and after the intervention. The 8 weeks of green vegetable drink consumption resulted in a significant decrease (p = 0.000, by paired t-test) in lymphocyte DNA damage expressed by TL (before: $63.13{pm}1.05$ vs after: $37.86{pm}10.83$, before: $66.73{pm}1.24$ vs after: $36.51{pm}1.13$), TM (before: $14.55{pm}0.61$ vs after: $6.61{pm}0.25$, before: $15.36{pm}0.45$ vs after: $6.65{pm}0.38$) and $\%$ DNA in tail (before: $19.7{pm}0.41$ vs after: $16.6{pm}0.37$, before: $20.6{pm}0.31$ vs after: $17.1{pm}0.5$) in both nonsmokers and smokers respectively. Vitamin C and TRAP level was not significantly changed after the supplementation. In conclusion, these results support the hypothesis that green vegetable drink exert a cancer-protective effect partially via a decrease in oxidative damage to DNA.