The Ba(HCOO)(2)-Fe(HCOO)(2)-H2O system has been studied by the solubility method at 25degreesC and formation of a new double salt with composition Ba2Fe(HCOO)(6).4H(2)O was established. The double salt has been characterized by X-ray powder diffraction and thermal analysis. Ba2Fe(HCOO)(6).4H(2)O is iSOStructural with the double salts Ba2Me(HCOO)(6).4H(2)O (Me Co, Ni, Cu, and Zn) and crystallizes in the triclinic system (space group P (1) over bar) with lattice parameters a = 8.902(3) Angstrom b = 7.125(2) Angstrom, c = 6.901(3) Angstrom, alpha = 98.85(5)degrees, beta = 108.81(4)degrees, and gamma = 82.47(3)degrees. The presence of two steps in the thermal dehydration process of the double salt has been established by means of DSC at lower heating rates. The enthalpy of dehydration has been determined.