Atmospheric dielectric barrier discharges (DBDs) are typically used for activation and modification of surfaces, sterilization, bioactivation and deposition of coating barriers. Atmospheric DBDs have the advantage that, at a relatively high pressure, a cold but chemically active plasma is created. Spectra from the ozone synthesis system, using oxygen gas, have been detected in the range 300–400 nm. The dependences of the spectral intensity on the discharge voltage and the oxygen pressure has been studied. The half-width of the detected lines has been found to be within 20 Å approximately. The electron temperature within a microdischarge has been estimated by using the relative intensity of the line-to-line ratio technique of the identified spectral lines. An average mean electrons temperature of 3.6 eV has been obtained and found to be insensitive to gas pressure variation.