A novel 3D tetrazole-bridged 3d-4f heterometallic MOF {(H3O)3[Gd3Mn2(Trz)4]·12H2O}n (1) with a hexanuclear [Gd6] cluster was obtained via in situ [2+3] cycloaddition reaction and structurally characterized, possessing good solvent and thermal stabilities, as well as a large magnetic entropy change -ΔS(m) = 40.3 J kg(-1) K(-1) for ΔH = 7 T at 2.0 K. To our knowledge, it is the first example of tetrazole-bridged 3d-4f heterometallic MOFs.