Abstract: The relationship between nicotine to nornicotine conversion, as well as nornicotine content, and the con-tents of myosmine and TSNA was investigated using burley TN90 samples of no-converter, low and high converter plants. The results showed that myosmine content increased linearly both in lamina and in midrib as nicotine conversion level and nornicotine content increased. When nicotine conversion rate was over 20%, myosmine content sur-passed anabasine content. Of the 4 main tobacco-specific nitrosamines, NNK, NAT and NAB contents didn't showsignificant difference among tobacco samples of different conversion levels; while NNN content increased sharply asthe nicotine conversion level raised, especially in midrib, the proportion of NNN in total TSNA increased while theothers decreased accordingly. In high converter plants, the NNN proportion may reach 90% of the total TSNA. In lamina, the content and proportion of NAT were higher than that of NNK, while in midrib, NNK was higher than NAT in content.