Stomach carcinoma is still the leading cause of cancer death in China and the second one in the world. Its possible causes include: A) chemical factors such as intragastric formation of N-nitroso compounds (NOC) and high salt intake; B ) biological factors such as infection of Helicobacter pylori and biotoxins intake; and C ) nutritional factors such as deficiency of vitamin C, selenium, and other antioxidants. Nitrogenous precursors of NOC, e.g., alkylamines, alkylureas, alkylguanidines, and alkylamides, occur widely in nature and potential nitrosating agents, e.g., nitrite (NO2-) and NOx (the gaseous oxides of nitrogen ) are similarly widespread. Relationship between exposure to NOC and causes of human cancer was investigated extensively ten years ago. Results indicated that the exposures of NOC might contribute to the occurrences of malignancy in the upper digestive tracts including stomachs. It was also observed that both high salt intake and deficiency of some micronutrients enhanced NOC-induced carcinogenicity. Recent studies show that infection of H. pylori can lead to atrophic gastritis and achlorhydria, and promote endogenous formation of NOC indirectly[1] . Much attention has been paid to stomach cancer and NOC regarding the characterization of natural N-nitrosamides in human environment in the 1990s.