In the present study, thin films consisting of quadrilateral nanoplates of CuO on the surface of a Cu plate were successfully synthesized in a two-dimensional micro space by the hydrothermal oxidation of a Cu plate using aqueous (NH₄)₂S₂O₈ solution as the oxidizer. Selective crystal growth was clearly observed in the two-dimensional micro space formed between the Al₂O₃ and the Cu plates, and a highly crystalline CuO quadrilateral nanoplate thin film was formed on the surface of the Cu plate that faced the Al₂O₃ plate. Similar experiments were performed by replacing the Al₂O₃ plate by Cu, Ti, or SUS316L plates as the substrate, to investigate the effect of the substrate facing the Cu plate. Using different substrates resulted in significant differences in the morphology of the CuO thin film on the Cu plate facing the substrate. In the past, parameters such as, the addition of structure directing agents or surfactants, varying the composition and concentration of reaction solutions, and changing the reaction temperature have been the principal methods used for controlling the structure of ceramic thin films at the nanoscale. The present study demonstrates that the use of a two-dimensional micro space can be extremely effective in controlling the nanostructure of thin films.