Abstract: Monodispersed dihydrated zinc oxalate (ZnC₂O₄·2H₂O) particles with characteristic morphology were synthesized by aging a mixed solution of zinc nitrate (Zn(NO₃)₂) and sodium oxalate (Na₂C₂O₄) in the presence of a citrate ligand, with an average flat size of approximately 10-15 μm. The important parameters, including the solution pH values and the concentration of the zinc ions and citrate ligand, were investigated using a series of experiments. It is verified that the citrate ligand significantly affects the morphology of zinc oxalate particles, probably via its multiple roles of chelating, dispersing, and selective absorption. Thermodynamic equilibrium of the distribution of zinc species in an aqueous solution of Zn(Ⅱ)-citrate-oxalate-H₂O was estimated to explain the experimental results and to clarify the size and morphological evolution mechanism of the precipitated particles.