A process of hexaamminerhodium trihydroxide, hexaammineplatinum (IV) tetrahydroxide, tetraammineplatinum (II) dihydroxide and tetraamminepalladium dihydroxide. Hexaamminerhodium trihydroxide is prepared by forming a solution of hexaamminerhodium (III) chloride by reacting a solution of rhodium (III) chloride and an excess amount of aqueous ammonia, heating the thus formed solution to impart thereto a pH of 7.5 to 8.0, and contacting the hexaamminerhodium (III) chloride solution with an anion exchange resin having an OH form. Hexaammineplatinum (IV) tetrahydroxide is prepared by dissolving ammonium chloroplatinate into aqueous ammonia, and contacting the resulting solution of hexaammineplatinum (IV) tetrachloride with an anion exchange resin having an OH form. Tetraammineplatinum (II) dihydroxide is prepared by contacting a solution of tetraammineplatinum (II) dichloride with an anion exchange resin having an OH form. Tetraamminepalladium dihydroxide is prepared by contacting a solution of tetraamminepalladium dichloride with an anion exchange resin having an OH form. The resulting product solutions have a remarkably reduced chloride ion concentration and exhibit high stability. Furthermore, a silver component is not required, such that purity of the respective product solutions is elevated.