The experimental study of the degradation of gaseous dielectrics after processing in the dielectric barrier discharge (DBD) is presented. Two pure gases trans-CF3CH=CHF (HFO-1234ze(E)), perfluoroketone CF3C(O)CF(CF3)2(C5K), and also the following mixtures 75 %HFO-1234ze(E):25 %N2, 12 %C5K:88 %N2, 18.5 %C5K: 81.5 %dry air, 9 %C5K:57.5 %HFO-1234ze(E):33.5 %N2, 9 %C5K:56 %HFO-1234ze (E):35 %CO2have been used as test-gases. A content of the decomposition products of the gases before and after a 5-h workout in the barrier discharge has been determined by means of the chromatography-mass spectrometry and gas chromatography methods. Dilution of C5K with dry air greatly increases the degree of conversion of the source gas in the barrier discharge. Dilution of HFO-1234ze(E) and C5K with nitrogen, and the use of ternary mixtures 9 %C5K:57.5 %HFO-1234ze(E):33.5 %N2and 9 %C5K:56 %HFO-1234ze(E): 35 %CO2significantly reduces the degree of conversion of the mixture compared with the source gases in the barrier discharge. After the DBD processing of two test-gases a large quantity of toxic C3F6 was found in pure C5K, and also a large number of highly toxic CF3CCH was found in pure HFO-1234ze(E). The least amount of toxic products after the DBD processing was detected in mixtures HFO-1234ze(E):N2and C5K:HFO-1234ze(E):N2. The mixture C5K:HFO-1234ze(E):N2has the best features among studied mixtures.