Objective: To study the expression of CD44s mRNA in the occurrence, development and invasion of gastric carcinoma (GC). Methods: The expressions of CD44s mRNA in 66 cases of GC, 25 cases of superficial gastritis and 25 cases of atypical hyperplasia were examined by in situ hybridization (ISH). Results: There was no expression of CD44s mRNA in the group of superficial gastritis; the positive rate was 20%(5/25) in the group of atypical hyperplasia and 62.12%(41/66) in the group of gastric carcinoma. The positive rate in poor differentiation group was significantly higher than that in well differentiation group (P＜0.05), and the positive rate of lymph node metastasis group was significantly higher than that in negative lymph node metastasis group(P＜0.05). Conclusion: The expression of CD44s mRNA was related to cell differentiation degree and lymph node metastasis, the activation of CD44s gene was related to strong invasion of cancer cells and poor prognosis.