Objective: To investigate the profile of 5-FU-induced apoptosis in tumor cell line and evaluate the usefulness of Annexin V and propidium iodide double staining for detecting apoptosis. Methods: Colon cancer cell line colo320 was incubated with 5-FU of different concentration for 2, 4,6, 8 and 12h respectively, apoptosis was measured using Hoechst33342 staining and a flow cytometry method that measures Annexin V and propidium iodide (PI) staining. Results: Apoptosis could be induced in colo 320 cell line by 5-FU,the percentage of AnnexinⅤ~+PI~-cells increased after being treated with 80ug/ml 5-FU for 4 h,both apoptotic and necrotic cell increased at 12h.Apoptotic cells were also identified by Hoechst33342 staining. Conclusion: Apoptosis induced by 5-Fu is time and dose dependent.Annexin V and PI double staining is a specific, sensitive, and quantitative method for analyzing apoptotic cells.