A catalyst for the selective oxidation of olefins in the presence of air or oxygen, comprising a compound of the formula (1) MoxOy(L)z  (1) where x is 1, 2 or 3, y is an integer from 0 to 2x+1, z is an integer from 1 to 2x, wherein the ligand L is a compound of the formula (2) or (3)  where n is 0 or 1, X is a nitrogen, oxygen or sulfur atom, Y is hydrogen, C1-C8-alkyl, C1-C8-alkoxy, F, Cl, Br, I, COOCH3, C6-C14-aryl or C3-C8-cycloalkyl, R3 and R4 form a ring containing from 4 to 8 carbon atoms onto which one or two aromatic rings may be fused, R1 and R2 are hydrogen, branched or straight-chain C1-C12-alkyl or branched or straight-chain C1-C12-haloalkyl which substitute the ring formed by R3 and R4 and/or the rings fused onto this ring, or the ligand L is a compound of the formula (4) or (5) where R is hydrogen, C1-C8-alkyl, C1-C8-alkoxy, COOCH3, carbonyl oxygen, C6-C14-aryl or C3-C8-cycloalkyl and n is 1 or 2 and m is from 1 to 6.