Planarization is often crucial to the implementation of three-dimensional devices and systems. By using a pressing process analogous to nanoimprint, the authors show that moderate to high aspect ratio (>= 3) photonic nanostructures in the form of one-dimensional and two-dimensional photonic crystals can be effectively planarized with thermally cured sol-gel or uv-curable nanoimprint resist materials. The planarization results are strongly dependent on parameters such as pressing pressure, hydrophobicity of feature surface, spin conditions for sol-gel, and dispense volume for uv-curable. High degree of planarization and complete filling of open features can be achieved through optimization of imprint parameters. Nanoimprint planarization may thus offer a simple, low cost, fast, and viable alternative planarization methodology.