Relationship between the size of Polyimide fine particles and some conditions in the reprecipitation method was investagatge. As a result, polyimide ultrafine particles with ca. 50 nm in size have been successfully fabricated through the "two-steps imidization", i.e. chemical imidization followed by thermal imidization of poly(amic acid) (PAA) precursor ultrafine particles prepared under an optimum reprecipitation condition.