Colloidal crystallization of poly(vinylidene fluoride) (PVDF) nanoparticles (NPs) and its beta-phase transformation were studied. The pristine PVDF NPs with an average diameter of 230 nm, consist of 46% alpha-phase and 54% amorphous PVDF. The PVDF NPs were assembled on a quartz substrate by means of vertical deposition method from a tetrahydrofuran dispersion of PVDF NPs with a few volume percentage of n-alkane. The resultant colloidal thin films displayed a pale-greenish structural with the selective reflection at around 550 nm wavelength due to closely packed PVDF NPs. The colloidal thin films Were immersed into an acetonitrile solution containing 2 wt % ionic liquid, subsequently air-dried, and thermally annealed at 140 degrees C, just below the melting point of the PVDF-IL blends. After annealing, the PVDF NPs partially transformed into its beta-phase with the volume percentages of alpha-, beta-, and amorphous phases of 22, 32, and 46%, respectively. The postannealed colloidal films stilt maintained the face-centered-cubic assembling structure of PVDF NPs, thus displaying the greenish structural color and selective reflection.