Background:Recent studies have showed that high homocysteine(Hcy)level can increase the risk of gastric cancer, but no related studies have been reported on role of Hcy in gastric precancerous diseases. Aims:To investigate the role of serum Hcy,folic acid and vitamin B12 in patients with gastric cancer and precancerous diseases. Methods:Eighty-six normal controls,46 atrophic gastritis,46 gastric ulcer,31 gastric polyp,52 gastric cancer patients diagnosed by gastroscopy and pathology were enrolled. Serum levels of Hcy,folic acid and vitamin B12 were determined,and their correlations with clinicopathological features in gastric cancer were analyzed. Results:Compared with normal controls, serum Hcy level in patients with atrophic gastritis and gastric cancer was significantly increased(P < 0. 05);serum folic acid and vitamin B12 levels in patients with gastric ulcer,gastric polyp and gastric cancer were significantly decreased(P <0. 05). Serum Hcy level in patients with gastric cancer was positively correlated with depth of tumor infiltration,TNM staging and lymph node metastasis(P < 0. 05),however,serum folic acid and vitamin B12 levels had no correlation with clinicopathological features. Conclusions:Hcy level is increased in chronic atrophic gastritis,gastric cancer;levels of folic acid and vitamin B12 are decreased in gastric ulcer,gastric polyp and gastric cancer. High level of Hcy is involved in infiltration and metastasis of gastric cancer. Intervention in patients with high level of Hcy,low levels of folic acid and vitamin B12 might be an effective strategy for the prevention and treatment of gastric cancer and precancerous diseases.