Abstract The preparation and analysis of the oxalato complex of manganese (IV), referred to as K2[Mn(OH)2(C2O4)2]·2H2O by Cartledge and Ericks, were reexamined. Measurements of magnetic moment confirmed the unusually low value, 2.48 B.M. at room temperature. The infrared spectra of the complex suggest the presence of oxide bridges between manganese atoms. The electrical conductance of aqueous solution of the complex salt at 0 °C has been measured in various concentrations. The results indicate that the complex anion is dimeric both in solid and in solution. The electronic spectra of the complex in powder and solution states were measured, and some decomposition processes discussed. It was proposed that the complex should be formulated as a dimer with two oxide bridges, [Mn2O2(C2O4)4]4−.