Two transition metal-antimony oxo-cluster based compounds, H5{MCd(H2O)6[M(H2O)3Co3SbVSb(μ3-O)8(l-tta)6]}·7H2O (1) (M = Cd0.5 + Co0.5) and H3K5(H2O)11{Cd(H2O)4[Cd(H2O)Fe4Cd2Sb6(μ4-O)5(μ3-O)3(l-tta)6][Cd(H2O)2Fe4Cd2Sb6(μ4-O)4(μ3-O)4(l-tta)6][Cd(H2O)2Fe4Cd2Sb6(μ4-O)4(μ3-O)4(l-tta)6Cd(H2O)5]}·17H2O (2) (L-H4tta = l-tartaric acid) were hydrothermally synthesized and characterized. Compound 1 features a [MCo3SbVSb(μ3-O)8(l-tta)6(H2O)3]9- cluster, while compound 2 contains three types of clusters, namely, [Cd(H2O)Fe4Cd2Sb6(μ4-O)5(μ3-O)3(l-tta)6]4-, [Cd(H2O)2Fe4Cd2Sb6(μ4-O)4(μ3-O)4(l-tta)6]4- and [Cd(H2O)2Fe4Cd2Sb6(μ4-O)4(μ3-O)4(l-tta)6Cd(H2O)5]2-. All the clusters are of sandwich-type with {Sb3(μ3-O)(l-tta)} scaffolds on the top and bottom. The Cd (and M in 1) ions interconnect the clusters into layered structures in both compounds. To the best of our knowledge, this is the first report of transition metal-antimony oxo-clusters that simultaneously contain the first-row and second-raw transition metal ions, and compound 1 represents the first example of such type of clusters that contain Sb(v). The two compounds exhibit proton conductivity with the values of 2.43 × 10-3 and 2.95 × 10-3 S cm-1 at 85 °C under 98% relative humidity, respectively.