The dinuclear tungsten(V)-W2O42+ (aq) dimer (structure 1) is readily oxidized to W (VI) by a number of oxyhalogen species in aqueous acidic media. Oxidizing agents, BrO3., HBrO2, HOCl2 and HOCl with excess reductant yield the corresponding halide ions, and reduction of ClO3. yield Cl-., even when the oxidant is in large excess. The reaction of IO3. is complicated by relatively rapid reaction between I-. and IO3. at low pH, which undergoes further slow reduction yielding I-2. Reduction of ClO3. and BrO3. are independent of hydrogen ion concentration in the range 0.1 - 1.0 M[H+], but reduction of the acids HBrO2, HClO2 and H5IO6 are found to be inverse-first order in [H+]. Hypochlorous acid appears to react via a [(W-V)(2)-ClOH] adduct, which undergoes deprotonation (PK=1.5), prior to electron transfer.