It is known that catechins, which abundantly present in green tea, can inhibit N-nitrosodialkylamine formation from dialkylamines and nitrite. These polyphenolic catechins in tea leaves are decreased during heat-mediated processes used to prepare black and brown teas. In this study, we investigated the inhibitory effects of aqueous extracts of various tea leaves on nitrosation of dimethylamine (only slowly nitrosatable), morpholine (nitrosatable at a medium rate), andN -methylaniline (rapidly nitrosatable). We measured catechin contents in the extracts by HPLC, trying to correlate the contents with the inhibitions. An extract of sencha, the most common green tea in Japan, showed strong inhibitory effects on nitrosation of dimethylamine and morpholine, and moderately strong inhibitory effects on that of N-methylaniline. This effect was apparently due to the pressure of catechins in the extract. Unexpectedly, extracts of hojicha, a roasted brown tea with very low catechin content, significantly inhibited nitrosation of morpholine and N-methylaniline. Interestingly, hojicha extract enhanced nitrosation of dimethylamine. Extracts of oolong tea and black tea, which are also low in catechin contents, showed similar inhibitory effects. These results suggest that not only catechins but also other components in the tea leaves can trap nitrous acid. We also examined the mutagenicity of these tea extracts by the Ames test after treatment with nitrite. No mutagenicity was detected in TA98 and TA100 with or without metabolic activation.