Direct dissolution of uranium carbide was found to be very effective when it was refluxed with an 18 M H2SO4‾15 M HNO3 (1:1) mixture. Clear solutions could be obtained within 1 h. Uranium-plutonium carbide, as well as PuO2 could also be dissolved in 1 to 2 h in the same way. Other nuclear materials, UO2 + C and UO2 + PuO2 + C, needed longer duration for complete dissolution. When the proportion of H2SO4 in the H2SO4‾HNO3 mixture was increased to 2:1, these materials also dissolved within 2 h. Quantitativeness of the dissolution was checked by the potentiometric determination of uranium and/or plutonium contents in these solutions. The results were in good agreement (±0.5%) when compared with the values obtained by the well-established dissolution method. During the fabrication of fuel (plutonium-rich mixed carbide) for the fast breeder test reactor, a large number of fuel samples were analyzed by using the above method of dissolution for the chemical quality control. Presuming the possibility of formation of small amounts of oxalic and mellitic (benzene hexacarboxylic) acids during the process of dissolution of carbides, the effect of the presence of these organic species on the potentiometric determination of uranium and plutonium was studied.