The objectives of this study were to determine the major components in tea leaves and tea extracts and to study the relationship between chemical content and antimutagenic activity of various tea extracts. The amount of catechins in various tea extracts was in the order: green tea (26.7%) > oolong tea (23.2%) > pouchong tea (15.8%) > black tea (4.3%). The amounts of caffeine and phenolic compounds in oolong tea extracts were 8.3 and 32.4%, respectively; these amounts were greater than those in the other three tea extracts. The ascorbic acid in green tea extracts was a little higher than in oolong and pouchong tea extracts. The amount of catechins in tea leaves also showed the order: nonfermented (green tea) > semifermented (pouchong tea and oolong tea) < fermented tea (black tea). The amounts of caffeine and phenolic compounds in oolong tea leaves are also higher than in other tea leaves. Besides water soluble components, tea leaves also contain several lipid soluble chemicals such as (β-carotene and tocopherols. The tea extracts, especially oolong and pouchong teas, markedly inhibited the mutagenicity of 2-amino-3-methylimidazo( 4,5-f)quinoline (IQ), 3-amino-l,4-dimethyl-5H-pyrido- (4,3-b)indole (Trp-P-1), 2-amino-6-methyl-dipyrido(l,2-a:3′,2′-d)imidazole (Glu-P-1), benzo[a]pyrene (B[a]P) and aflatoxin B1 (AFB1). The inhibitory effect of tea extracts against the mutagenicity of IQ and Glu-P-1 in Salmonella typhimurium TA100 showed a significant (P < 0.05) correlation to the contents of catechins and ascorbic acid. The antimutagenic activity of tea extracts to Trp-P-1 in TA98 or TA100 was well correlated (P < 0.05) to the caffeine contents. No significant (P > 0.05) correlation was found between the antimutagenicity of tea extracts to B[a]P and AFB1 in TA100 and the content of major components in tea extracts.