5-Fluorouracil(5-FU)has been widely used to treat gastrointestinal,head,neck,chest and ovarian malignant tu-mors since 1957. As an analogue of pyrimidine,5-FU plays anti-cancer roles by inhibiting thymioylate synthase and integrating its me-tabolites into DNA and RNA. Although 5-FU is one of the first-line therapeutic compounds for gastrointestinal malignant tumor as a sin-gle drug or in combination with other drugs,its effectiveness is hindered by its low efficiency,which may be due to chemotherapy re-sistance. 5-FU chemotherapy resistance may stem from enzyme abnormality,genetic abnormality and tumor microenvironment. In this paper,we make a review about 5-FU actions and the mechanisms underlying chemotherapy resistance.

0.05);the disappearance rate of varices of fundus of stomach and esophagus in the combined devascularization group was higher than that in control group(P0.05).The long-term(fourth to seventh year)survived rate of the combined devascularization group was higher than that of control group(98.3% in the combined devascularization group,90.0% in control group)(P