Ionization energies of the higher fullerenes C-n (n = 70-106) were measured by means of the ion-molecular equilibria-Knudsen Cell mass spectrometry method. The obtained values were found to decrease with the size, going from LE(C-70) = 7.36 eV down to IE(C-105) = 6.92 eV, with unexpectedly low IE(C-74) 7.13 eV. A good correlation of the experimental results with the theoretical values is demonstrated. A simple model describing the ionization properties dependence from the fullerene size is proposed.