An iron(Ⅱ) formate [H3CO3][Fe(HCO2)3] (1) has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction analysis. Complex 1 crystallizes in the orthorhombic system, space group Pnna with a = 8.4130(4), b = 11.8306(6), c = 8.9468(4)A, a = 106.527(4), β = 105.876(4), 7 = 103.173(4)°, Mr= 253.94, V= 890.48(7) A3, Z= 4, Dc = 1.894 g/cm3,μ = 1.721 mm^-1, F(000) = 512, Rint = 0.0164, the final R = 0.0323 and wR = 0.0998 for 979 observed reflections (I 〉 2σ(I)). 1 exhibits a 3D open microporous framework formed by formate anions bridging Fe(Ⅱ) ions.