A novel millimeter wave quadruple-push oscillator is presented in this paper. The quadruple-push oscillator consists of four identical sub-circuits and a ring resonator that is used as a common resonator. It is well known that there are two orthogonal resonant modes on a one-wavelength ring resonator. According to this resonant characteristic, two orthogonal push-push oscillations can be set up in the quadruple-push oscillator, and there is a phase difference of 90° among four sub-circuits due to nonlinear performance. Therefore, the four identical sub-circuits can oscillate at the same fundamental frequency f 0 , and the fundamental oscillating signal of one sub-circuit has phase differences of 90°, 180° and 270° to that of the others, and the desired fourth harmonic signals can be combined due to their in phase relations, and the undesired fundamental signals, the second harmonic signals, the third harmonic signals and so on can be suppressed when the oscillating signals of the four sub-circuits are added in phase. The principle is firstly explained in this paper, and is proved in the experiment of a Ka-band quadruple-push oscillator. The measured output power of the desired fourth harmonic signal (4 f 0 ) was +1.67 dBm at the frequency of 35.8 GHz. The measured suppression of the undesired signals of the fundamental signal (f 0 ). the second harmonic signal (2 f 0 ), the third harmonic signal (3 f 0 ) and the fifth harmonic signal (5 f 0 ) were -18.0dBc, -17.9dBc, -17.8dBc and -35.5dBc, respectively. The measured phase noise performances at 35.8 GHz were -104.0 dBc/Hz and -82.3 dBc/Hz at the offset frequency of 1 MHz and 100kHz, respectively.