OBJECTIVE： To analyze and summarize the drug interaction of warfarin with antitumor drugs and adjunctive drugs， and to provide reference for safety of clinical drug use. METHODS： By retrospective analysis， medical orders of inpatient receiving warfarin were collected from hospital information system during Jan. 2006－Dec. 2015. General information of patients，indications，usage and dosage of warfarin，INR values were extracted and summarizcd according to drug interacien evaluation criteria of MICROMEDEX 2.0 database， and then confirmed by reviewing related literatures. RESULTS： Totally 72 medical orders were included，involving 56 patients. Dosage of warfarin in 14 medical orders had adjusted in antitumor treatment. MICROMEDEX 2.0 evaluation involved drug interaction of 17 drugs with warfarin. Among them， erlotinib， fluorouracil， capecitabine， etoposide， carboplatin， vincristine and ibuprofen would seriously interact with warfarin. CONCLUSIONS： Warfarin interacts with a variety of antitumor drugs and adjunctive drugs. When warfarin combine with antitumor drugs and adjunctive drugs， medical workers should closely monitor INR values， and complete the prevention measures to ensure the safety of drug use.