Abstract: Tobacco-specific nitrosamines (TSNA)is a group of potential carcinogens which have been found in tobacco, tobacco products, and cigarette smoke only.The precursors are tobacco alkaloids, nitrate and nitrite. The pre-cured tobacco leaves of growing and ripeness do not contain TSNA, and they are formed and accumulated during curing, aging after harvesting. All factors of effective precursors will affect their form and accumulation of TSNA. We can decrease TSNA by ways of reducing level of precursors.