Four two-dimensional fully reduced polyoxovanadates, namely, [Cd(DAP)2]4[HV(III)3V(IV)18P6O60(DAP)3(HOCH2CH2OH)]·10H2O (1), [Cd(DAP)2]4[HV(III)3V(IV)18P6O60(DAP)3(CH3OH)]·11H2O (2), [Cd(DAP)2]4[HV(III)3V(IV)18P6O60(DAP)3(CH3CH2OH)]·4H2O (3) and Co(III)(DAP)3[Co(II)(DAP)2]3[V(III)3V(IV)18P6O60(DAP)3(HOCH2CH2OH)]·14H2O (4) were synthesized by virtue of the reducing power of alkylamine in hydrothermal conditions. Single-crystal X-ray structural analysis, magnetic measurement, IR spectroscopy, elemental analysis, and thermogravimetric measurements were performed to analyze the structures and properties of these four compounds. Structural analysis indicates that the four compounds contain the same huge low-valent vanadium oxide anion cages [V(III)3V(IV)18P6O60(DAP)3](9-), and the cages can catch different guest molecules. Four cages are linked by Co or Cd atoms to form a four-membered ring, while adjacent four-membered rings are connected to each other by sharing edges to make an inorganic-organic hybrid layer. The magnetic susceptibility measurements of four compounds indicate ferrimagnetic interactions between vanadium ions.