Mercury(II) oxide has been reacted with D-gluconic acid (Gl) in an aqueous solution at a molar ratio of the reagents equal to 1: 2 to obtain mercury complex Hg2(C6H11O7)2 (I). The product isolated has been studied by elemental analysis, molar conductivity, IR, electronic, and NMR spectroscopy, and X-ray diffraction. The data obtained indicate that the compound contains the binuclear cation (Hg2)2+. It has been found that the complex has a chelate structure. Each mercury atom in I is connected with two oxygen atoms: one from the carbon atom of the carboxyl group and another from the hydroxyl group at the second carbon atom in the Gl molecule. Two gluconate ions in the complex have different configurations. Toxicity of I is ten times less than the toxicity of the starting mercury compound. Reacting Gl with the oxide of divalent mercury in an aqueous medium decreased he toxicity of the mercury compound due to its reduction to a formally monovalent state. The results can be useful for studying mercury detoxification and the application of Gl.