The high-valence tin-oxo clusters are of great significance because of their structural diversity and potential applications in many fields, e.g., catalysis, extreme ultraviolet (EUV) lithography, and so on. The synthesis of high-nuclearity tin-oxo clusters remains a great challenge currently, since the key inorganic SnxOy core with Sn4+ ions could not be obtained only by the in situ Sn-C bond cleavage in organic tin sources. In this context, we synthesize three organic-inorganic hybrid Sn18-oxo clusters, [(BuSn)12Sn6(μ3-O)20(ba)12(PhPO3)4] (Bu = butyl, Hba = benzoic acid), [(BuSn)12Sn6(μ3-O)20(pmba)12(PhPO3)4]·2CH3CN·2H2O (Hpmba = p-toluic acid), and [(BuSn)12Sn6(μ3-O)20(ptba)12(PhPO3)4]·2CH3CN·2iPrOH·2H2O (Hptba = p-tert-butyl benzoic acid), as well as one Sn6-oxo cluster [(BuSn)6(μ3-O)2(μ2-OH)4(pnba)6(PhPO3)2] (Sn6) (Hpnba = p-nitrobenzoic acid) by combining an inorganic precursor (SnCl4) with an organic one (butyltin hydroxide oxide). It is shown that an inorganic dicyclo-chain-like Sn6O8 core encapsulated in a U-shaped dodecanuclear butyltin-oxo ring plays an important role in the construction of Sn18-oxo clusters and that the use of a ligand with an electron-withdrawing group reduces the nuclearity of clusters to Sn6. Moreover, electrocatalytic CO2 reduction studies confirm that the electrocatalytic activities of the Sn18 clusters are superior to those of the Sn6 cluster, probably due to the hybrid organotin-inorganotin structures. Our work not only opens a new way for constructing high-nuclearity tin-oxo clusters but also is helpful in deeply revealing the structure-properties relationship of tin-oxo clusters.