Fluorescence intermittency (blinking) of semiconductor nanocrystals (NCs) is interpreted in terms of single photon-counting at high temporal resolution of tens of kiloframes per second (kfps) by fast imaging on ZnS overcoated CdSe (CdSe/ZnS) NCs. We report herein a characterization method based on the threshold resulting from a double exponential distribution as a function of the photon interval to discriminate between “on” (bright) and “off” (dark) states. Histograms of both the resolved “on” and “off” lengths show that they obey single Poisson distributions with their duration constants, contrary to the conventional power-law distributions. We suggest that this characterization gives us more potential power to elucidate blinking kinetics of single CdSe/ZnS NCs on their physicochemical surroundings. [DOI: 10.1380/ejssnt.2009.701]