Abstract: 5-Fluorouracil (5-FU) is one of the most widely used chemotherapeutic agents for various solid tumors in-cluding breast cancer, colorectal cancer (CRC), and gastric cancer. Unfortunately, some patients have a poor response, possibly owing to clinical resistance of the chemotherapy. Understanding the mechanisms of resistance to 5-FU would al -low better selection of patients for 5-FU therapy and allow personalized therapeutics to be designed to overcome resis -tance. Recently there have been many studies done and much progress made in 5-FU biological control, pro-drug develop -ment and delivery methods. For example, MUC1, dihydropyrimidine dehydrogenase, O- 6-methylguanine-DNA methyltrans -ferase, Heat shock protein 27, Heat shock protein 40, Epidermal growth factor receptor vIII, and others have been found to be related to low 5-FU efficacy. On the other hand orotate phosphoribosyltransferase , calcium-sensing receptor, 5-chloro- 2, 4-dihydroxypyridine, prostate apoptosis response protein 4, tissue inhibitor of matrix-metalloproteinases 1, tyroservatide, 5-azadeoxycytidine, PG490 , Rosiglitazone, Rapamycin, and various herbal medicines have been found to promote 5-FU ef -ficacy. There are also several serum biomarkers for monitoring the treatment response of 5-FU including regenerating is-let-derived family member 4, insulin-like growth factor binding protein 3, a proliferation-inducing ligand/tumor necrosis factor superfamily, and TNFSF 13. The latest progress in understanding the molecular mechanisms of 5-FU resistance and sensitivity and identifying predictive biomarkers, as well as developing research trends, are reviewed in this paper.