The optical-optical double resonance multiphoton ionization (OODR-MPI) technique has been applied to the study of the Rydberg states of nitrogen dioxide. The results show that NO2 molecule is ionized though a 1+3+1 double resonance multiphoton ionization process in 605—675nm probe wavelength region. The ionization pathway is: NO2(X2A1)hν1NO2(A2B2)3hν2NO2(3pσu)hν2NO22+e. The OODR-MPI spectrum corresponds to the excitation of NO2 3pσu Rydberg state by a three photon process. The value　ω1=(1422.5±23.5) cm-1 and ω2＝(590.5±4.9) cm-1 of symmetric stretching and bending vibration frequencies of this Rydberg state are presented. The position of the band origin and the quantum defect of 3pσu Rydberg state are obtained to be (58331±71) cm-1 and 0.69, respectively.