Thiosulfate (S2O32-) can be quantitatively oxidized to sulfate (SO42-) without production of elemental sulfur (S-o) by a two-step anodic process at glassy carbon electrodes in 1.0M NaOAc/1.0M HOAc buffer (pH 5). The first step, at 1.0 V vs. SCE, converts S2O32- to tetrathionate (S4O62-). The second step, at 1.6 V vs. SCE, converts S4O62- to S4O2-. Addition of bromide (Br-) to S2O32- solutions expedites the desired conversion, presumably because of homogeneous oxidations by bromine (Br-2) generated by anodic oxidation of Br-.