Abstract: Objective: To explore the molecular biological foundation of the different clinical manifestations of gastric cancer between the young and the old. Methods: A total of 57 cases, 41 cases older than 60 and 16 cases younger than 35, were selected randomly. The mRNA expression of heparanase, MMP- 7, S100A4 and nm23H1 genes in the primary gastric lesions was detected by RT- PCR.The difference in clinicopathological features and genetics between the two groups was compared. Results: In patients younger than 35, poorly differentiated carcinoma, signet- ring cell carcinoma and mucinous adenocarcinoma were the most common types; highly and/or moderately differentiated carcinoma and tubular or papillary adenocarcinoma were most frequently observed in the patients older than 60,with a significant difference between the two age groups (P<0.05). Compared to that of the elder patients, the younger patients had higher expression of S100A4 and lower expression of nm23H1 (P<0.05).Among the younger patients, nm23H1 expression was lower in cases with serosa involvement than in cases without serosa involvement. In the younger patients, MMP- 7 expression was higher in the highly and/or moderately differentiated cases than in the poorly differentiated cases, and S100A4 expression was higher in patients with lymph node metastasis than in patients without metastasis (P<0.05). Among the older patients, the nm23H1 expression level in the poorly differentiated carcinomas was lower than that in the highly and/or moderately differentiated carcinomas, heparanase expression was higher in pa-tients with lymph node metastasis, and MMP- 7 expression in patients with significant lymph node metastasis and small node fusion was higher than that in patients with less lymph node metastasis and large node fusion (P<0.05). Conclusion: The clinicopathological features of gastric cancer differ between younger and older patients. S100A4, MMP- 7, heparanase and nm23H1 may be important genes that control the different biological behaviors in the two age groups. Examining the expression of these genes can contribute to an evaluation of the differentiation, infiltration and metastasis of gastric cancer.