Abstract: A method and a system for measuring the number of hyperfine particles comprising the step in which an air aerosol containing fine particles is led into a saturated vapor chamber and a high temperature saturated vapor chamber, respectively, to produce saturated vapor aerosols, the step in which the two saturated vapor aerosols produced as aforenoted are led into a mixing chamber, so that the aforementioned vapor is condensed on the aerosol particles as the nuclei, thereby achieving growth of the aforementioned fine particles, and the step for measuring the number of the said fine particles grown in that way.