Late-model ionic clusters of KNO3 were formed under the conditions of electrospray ionization. A series of peaks of the ionic clusters could be observed in the electrospray ionization mass spectra(ESIMS). The general formulae of the ionic clusters were deduced to be K+(KNO3)n and NO-3(KNO3)m. By referring to the crystal structure of KNO3, the possible configurations of these new typical ionic clusters were speculated based on the calculated data by means of the Gaussian-94x computer program.