Abstract: The invention relates to the use of an uridine derivative of formula (I); wherein —R1 represents monohalogenated alkynyl or dihalogenated alkenyl; —R2 is chosen from among hydrogen, hydroxyl, O-alkyl, O—CO alkyl and halogen; —R3 is chosen from among hydrogen, hydroxyl, O-alkyl, O—CO alkyl, halogen, SH, S-alkyl and N3; and —R4 is chosen from among hydroxyl, O-alkyl, O—CO alkyl, O-phosphate, O-diphosphate, O-triphosphate and O phosphonate, as well as its possible tautomers, its possible pharmaceutically acceptable addition salts with an acid or a base, and its N-oxide forms, for the preparation of a drug having antiviral activity against a Flaviviridae.