The first organofunctionalized mixed-valent polyoxo-30-molybdate wheel, [MoVI18MoV12O84{AsO2(CH3)2}18]18- (Mo30), was synthesized in aqueous, mildly acidic conditions, and upon further acidification, the neutral tetramolybdenum(V) oxo cluster [MoV4O8{AsO2(CH3)2}4] (Mo4) was obtained. Single-crystal X-ray diffraction (XRD) revealed that Mo30 comprises 18 MoVI and 12 MoV ions arranged in a cyclic fashion with alternating {MoV2} and {MoVI3} groups, which are capped by 18 dimethylarsinate ligands, resulting in a novel polyoxo-30-molybdate wheel with a central cavity of ∼1.5 nm. On the other hand, Mo4 has a distorted-cubic structure, with the corners of the cube being occupied by alternating MoV ions and oxo ligands. The compounds were characterized in solution by 1H and 13C NMR and UV-vis spectroscopy and in the solid state by X-ray photoelectron spectroscopy and powder XRD. Mo30 represents a novel type of polyanionic cycle with manyfold possibilities regarding host-guest chemistry.