Ignition characteristics of hydrocarbon fuels such as methane(CH4) and ethylene(C2H4) by a plasma jet (PJ) torch in a supersonic flow were investigated and compared with that of hydrogen (H2). The main airflow Mach number was 2.3, and the stagnation pressure and temperature corresponded to atmospheric condition. Nitrogen(N2), oxygen(O2), and N2/H2 mixtures were tested as feedstocks of the PJ torch. The wall pressure on the bottom wall was measured for judgment of the success of ignition. In the experimental result, the superiority of the O2 PJ to other PJs was remarkable for all fuels. However, this superiority of the O2 PJ could not be explained by the existence of O radicals. The effect of addition of radicals to ignition delay time and burning velocity was not so large, and the effect did not strongly depend on the kind of radical. On the other hand, the order of pressure increase by combustion was H2, C2H4, and CH4 for the same equivalence ratio. Even if the heat release of complete reaction of H2 was about 1.1 times of that of C2H4, the pressure increase by combustion of H2 was substantially larger than that of C2H4. This result indicated that the heat release of hydrocarbon fuels was small because of incompleteness of combustion reaction in the test section. Moreover, the effect of addition of CH4 to feedstock was investigated. The increase in the mole fraction of CH4 in the feedstock resulted in the worse performance as igniter than the N2 PJ, though the H radical concentration was increased with the mole fraction of CH4.