We report a fabrication of densely packed polydiacetylene nanocrystal film using a liquid-liquid interface. Polydiacetylene (pDCHD) nanocrystals was dispersed into water solution by reprecipitation method from a good solvent. Then, hexane was added to the water dispersion to create the liquid-liquid interface. pDCHD nanocrystals were assembled at the interface, when ethanol was added to the pDCHD water dispersion-hexane solution. The assembled film was transferred onto a solid substrate and the film morphology was observed by scanning electron microscope (SEM). With addition of 10 vol% of ethanol to 2.5 mM of pDCHD water dispersion-hexane solution, a densely packed pDCHD film is fabricated. Optical and electrical properties of the pDCHD film are discussed by UV-vis spectroscopy and current-voltage measurement.