The synthesis of condensation products of 4-hydroxycoumarin and nitro-substituted aromatic aldehydes as well as oximes of drugs with anticoagulant activity is described. The acute toxicity of the compounds was studied in mice by oral and intraperitoneal administration. A comparative pharmacological study of the in vivo anticoagulant effects of Warfarin derivatives showed that the new compounds have different anticoagulant activity. 4-Hydroxy-3-[1- (4-chlorophenyl)-3-oxobutyl]-2H-1-benzopyran-2-one, oxime 3 showed anticoagulant effect similar to Warfarin and Coumachlor, but its acute toxicity was higher than that of the reference drugs.