Objective: Many patients with metastatic colorectal cancer (MCRC) cannot afford the targeted therapy in China. There is no standard treatment when these patients whose tumors relapsed following the first- and second- line chemotherapy. The goal of the present study is to evaluate the efficacy and safety of continuous intravenous infusion (CIV) of low-dose 5-fluorouracil5-FUfor heavily pretreated patients with MCRC. Methods: Twenty-three heavily pretreated patients with MCRC received 5-FU 200 mg/m2 per day as CIV for more than 30 days. Efficacy and safety was evaluated after one cycle of chemotherapy. Results: No patient achieved complete response (CR), 2 patients partial response (PR), 8 patients stable disease (SD), and 13 patients progression disease (PD). Response rate (RR) was 8.7%, disease control rateCR+PR+SD was 43.5%Toxicity was mild. Conclusion: This study showed that continuous venous infusion of low-dose 5-fluorouracil was moderately active and well tolerated in heavily pretreated patients with MCRC.