Yb³⁺/Er³⁺ co-doped yttrium-based coordination polymer (CP) hierarchical micro/nanostructures constructed from well-stacked multilayers have been successfully fabricated on a large scale through a self-assembly process under hydrothermal conditions, among which allantoin with multiple N- and O-donor atoms was employed as an organic ligand. The as-prepared products were well characterized and analyzed. It turns out that the superstructures with well-defined morphology are built from nanoparticles with the size of 40 nm. The nanocrystals aligned with each other resulting in the formation of a multi-layered hierarchical structure. The detailed formation mechanism of the unique CP hierarchical micro/nanostructures was proposed. Moreover, the corresponding Y₂O₃:Yb³⁺,Er³⁺ hierarchical micro/nanostructures were obtained by heating the precursors at 800 °C for 4 h in air. The upconversion luminescence properties of the products were also investigated.