Fission-produced 131I and 103Ru radionuclides have been separated sequentially by distillation from H2SO4 of controlled chemical composition. The thermal-neutron irradiated uranium trioxide targets were digested in 2M NaOH solution and then, the supernatant solution was acidified to 20% H2SO4 with addition of a few drops of H2O2 solution. On boiling for 3.5 hours, ≥99.99%131I was volatilized, passed through 3M H2SO4 traps, and then collected in 0.1M NaOH + 0.01% Na2S2O3 solution with a recovery yield of 73.6%. The product radionuclide had high radiochemical and radionuclidic purities. After separation of 131I, the fission-product solution was acidified to 40% H2SO4 acid containing KMnO4 as an oxidant and boiled for 40 minutes. Ruthenium nuclides were volatilized and collected in 0.1M NaOH solution. Gamma-ray spectrometry showed that the separation and the recovery yields of 103Ru were ≥99.99 and 65%, respectively, with ~92% radionuclidic purity, measured immediately after separation. The radionuclides of 132I and 106Rh were the main contaminants detected in the obtained 103Ru product solution