N-Acylated N-phenyl-aminotetrahydro-2-furanones of the formula ##STR1## wherein R represents C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy or halogen,R.sub.1 represents C.sub.1 -C.sub.3 -alkyl, C.sub.1 -C.sub.4 -alkoxy or halogen,R.sub.2 represents hydrogen, C.sub.1 -C.sub.3 -alkyl, C.sub.1 -C.sub.4 -alkoxy or halogen,R.sub.3 represents hydrogen or methyl, with the total number of C atoms of the substituents R, R.sub.1, R.sub.2 and R.sub.3 in the phenyl ring not exceeding the number 8,R.sub.4 represents hydrogen or methyl, whileR.sub.5 represents one of the following groups: an alkythioalkyl or alkoxyalkyl group having 2 to 5 carbon atoms or an alkoxyalkoxymethyl group having a maximum of 6 carbon atoms, a 2-furanyl or 2-tetrahydrofuranyl group optionally substituted by halogen, a 1,2,4-triazolylmethyl group, a 1,2-pyrazolylmethyl group, or a group -CH.sub.2 -OR.sub.6 in which R.sub.6 represents a 5- or 6-membered heterocyclic having oxygen as the hetero atom are valuable fungicidal active substances. They can be used as fungicidal compositions, particularly for combating phytopathogenic fungi, e.g. against downy mildew on potatoes, tomotoes, grape vines and sugar beet and other plants. The novel compounds have a systemic action.