Abstract: In order to investigate the expression of p21 protein in gastric precancerous lesions, gastric cancer (GC) and HP positive patients, 20 biopsy specimens of GC,22 biopsy specimens of the dysplasia, 30 biopsy specimens from the intestinal metaplasia (IM) were examined by immunohistochemical method (LSAB system). The result showed that: 13(65. 0%) of GC, 12(54. 5%) of displasia and 11 (36. 6%) of IM were positive for p21 staining; in all biopsy specimens, the positive rates of p21in HP positive patients was 41. 6% (30/72), the expression of p21 in HP positive patients was significantly higher than that in HP negitive patients (P0.01). The results indicate that there is corrlation between HP infection and p21, and HP infection maybe one of gastrocarcinogenesis mechanisms through mutation of p21 gene.