Abstract: Objective: To investigate the relationship between the expression levels of uridine phosphorylase (UP) gene and the prognosis of patients with the gastric, colon and lung carcinomas. Methods: The mRNA level of UP gene was examined using RT-PCR in 28 cases of stomach carcinoma, 14 lung cancer and 22 colon carcinoma. Results: Among the 28 paired gastric samples, 20 showed higher expression level in tumors than in normal surrounding tissues and 8 cases showed equal or lower levels in the tumors. All the gastric patients received 5-Fu before and/or after the surgical resection and the prognosis of the patients whose UP gene expression in tumors was increased was relatively better than that with equal or less UP gene expression in the tumors. In contrast, most of patients with colon carcinoma (16 cases ) and all with lung cancer (14 in total) did not receive 5-Fu and majority of the colon (12 cases) and lung (10 cases) specimens showed a lower expression in the cancerous region. Thedifferentialexpressionbetweenthecancerousandnon-cancerousregionsinthepatientswithcolon and lung cancer was not related with the prognosis. Conclusion: These data suggest that the paired expression level ofUP gene in gastric cancer is a possible prognostic marker for the patients whoreceived 5-Fu.