Objective:To observe the clinical efficacy of Modified Weichang’an Decoction combined with 5-fluorouracil based chemotherapy in treating elderly patients with stage Ⅳ colorectal cancer. Methods 133 elderly patients with stage Ⅳ colorectal cancer were divided into the treatment group (68 cases) and control group (65 cases). All patients were treated with 5-fluorouracil based chemotherapy for 3 courses. In addition,the treatment group was orally treated with Modified Weichang’an Decoction. The short-term efficacy,toxic and adverse reactions,quality of life and overall survival in the two groups were compared.  Results:①In short-term efficacy,there were no statistically significant differences on the total effective rate and disease control rate between the two groups(P>0.05). ②The life quality of patients in the treatment group was better than that in the control group(P<0.01). ③The median PFS and median OS in the treatment group were significantly longer than those in the control group(P<0.05). ④The toxic and adverse reactions such as leukocyte reduction and peripheral neurotoxicity in the treatment group were less than those in the control group(P<0.05,P<0.01).  Conclusion: Modified Weichang’an Decoction combined with 5-fluorouracil based chemotherapy can enhance the short-term efficacy,reduce the toxic and adverse reactions,improve the life quality and prolong the survival in treating elderly patients with stage Ⅳ colorectal cancer.