Abstract: Objective In order to study the preventive effect of tea on DNA damage induced by cigarette smoking and to provide evidence on the protective effects of tea in human cancer.Methods Based micronuclei frequency and chromosome aberrations frequency of peripheral bloodly mphocytes as end point,the effect of mixed tea on smoke-induced DNA damage was investigated in 46 smokers in a six month,double-blind and randomized placebo-controlled intervention trial.Results A kind of mixed tea given in an oral dose of 3g/day for 6 months,significantly decreased the micronucleii formation and chromosome aberrations frequency in lymphocytes.In contrast,there was no significant change in the micronuclei frequency and chromosome aberration frequency after 6 months in the placebo group.Conclusion The results indicated that mixed tea may reduce cancer risk by preventing DNA damage in human induced by cigarette smoking and have preventive effect on human cancer.