Solution synthesis of optoelectronic components has the advantages of processability, bandgap tuning, and large-scale manufacturing potential. The synthesis of monodispersed rhombs in solution, however, has rarely been reported, even though rhombs are promising for realizing unique optical functions in integrated optoelectronics. We present in this article our success in developing a facile chemical method that used two polyols to generate nearly monodispersed metal-organic rhombic platelets. The success lies on the careful selection of precursors of proper oxidation states and the optimization of both the thermodynamic and the kinetic conditions for synthesis. Cuprous acetate, which acted as a heterogeneous nucleation agent, was dispersed in ethylene glycol, which acted as a stabilizer, a ligand, and a monomer for the formation of polymeric glycolates. By adjusting the volume ratio of polyethylene glycol (PEG) to ethylene glycol and the polymer size of PEG, rhombic platelets of 200-580 nm in side length and 170-240 nm in thickness were synthesized with aid of suitable structure-directing and dispersing agents. Energy-dispersive X-ray spectroscopy and FT-IR analyses revealed that the rhombic platelets were mainly composed of copper glycolate polymer chains. Knowledge obtained from this study can be expected to be applied to and to shed light on broad research topics concerning novel metal-organic nanostructure syntheses.