Abstract: Oleic acid-capped nanocrystals (nano ZrO₂) were fabricated via two-phase approach, modified and grafted onto polyamic acid (PAA). After the imidization of nano ZrO₂/PAA, nano ZrO₂/polyamide (PI) ultra-thin composite films were finally obtained. The nanocrystals and nano ZrO₂/PI ultra-thin composite films were characterized by TEM, XRD, FTIR and SEM, and the dielectric properties of the nano ZrO₂/PI ultra-thin composite films were also exploited. The results demonstrate the nano-size (about 5.0 nm) and mono-dispersity of ZrO₂, the morphology and crystallinity of the nanocrystals are not negatively influenced by modification or grafting. The nanocrystals are homogenously dispersed in the bulk of PI. The dielectric properties of nano ZrO₂/PI ultra-thin composite films are influenced by the mass fraction of nanocrystals and the filming condition (i.e., imidization temperature). With a PAA:ZrO₂ mass ratio of 2:3 and aimidization temperature of 320℃, the dielectric constant exhibites the maximum, around twice that of pure PI thin films. Overall, nano ZrO₂/PI ultra-thin composite film fabrication method (general nanocrystal preparation-modification-grafting-imidization) exhibites its efficiency, feasibility, flexibility and versatility. This method can be extended by evolving other nanoparticles with high dielectric constant, tailor the properties by tuning the content of nanoparticles and filming condition, and obtain high dielectric constant composite films with low cost and pollution.