The first structurally characterised oxomolybdenum(V) complexes with thienyl carboxylate ligands were prepared by the reaction of [Mo 2 O 3 (C 5 H 7 O 2 ) 4 ] or (NH 4 ) 2 [MoOCl 5 ] with the corresponding acid (2-thiophenecarboxylic, 5-methyl-2-thiophenecarboxylic or 3-(3-thienyl)acrylic acid). Complexes [Mo 2 O 3 (μ-OC 2 H 5 )(μ-O 2 CR)(C 5 H 7 O 2 ) 2 ](R=–C 4 H 3 S (1), –C 4 H 2 S(CH 3 ) (2) or –CHCHC 4 H 3 S (3)) were obtained upon substitution of two acetylacetonate ligands from [Mo 2 O 3 (C 5 H 7 O 2 ) 4 ] with RCOO − in dry ethanol. Reactions of (NH 4 ) 2 [MoOCl 5 ] with the corresponding thienyl carboxylic acid in the presence of γ-picoline (C 6 H 7 N) yielded complexes (C 6 H 7 NH)[Mo 2 O 4 (μ-O 2 CR)Cl 2 (C 6 H 7 N) 2 ] (R=–C 4 H 3 S (4), –C 4 H 2 S(CH 3 ) (5) or –CHCHC 4 H 3 S (6)). All of the six new complexes were characterised as dinuclear. The molecular structures of 1, 3, 4·0.5CH 3 CN and 5 were determined by the single crystal X-ray diffraction method. In the complexes the two molybdenum atoms are doubly bridged either by one oxygen and one ethoxy-oxygen, or alternatively by two oxo-oxygens, and are additionally bridged by the thienyl carboxylate ion in a didentate bridging manner. All complexes were further characterised by means of chemical analysis, IR spectroscopy, TG and in some cases by the one and two-dimensional NMR method.