It is well known that the efficiency of ozone synthesis based on oxygen molar fraction is 2.5 times as large when air is used rather than pure oxygen. One of the reasons is considered to be the dissociation of oxygen molecules by excited nitrogen molecules. In this paper, the effects of gas mixture in ozone synthesis were studied experimentally. High efficiency of ozone synthesis could not be obtained in high N2 concentration, bacause the addition of N2 to O2 formed gaseous NOx. However, by the addition of CO2, high efficiency was obtained on account of the formation of oxygen atoms due to the dissociation of CO2. By the addition of Ar, the discharge inception voltage was decreased, and accordingly a number of small discharges were generated, thus making the efficiency high. Oxygen gas was exposed to luminescence due to discharging gases. The amount of ozone formed depended on the wavelength and intensity of the discharge luminescence.