Characteristics of the -induced chain reaction between sulfur dioxide and molecular oxygen in perchloric and sulfuric acid media in the presence of Ce(III) ions have been studied. The concentration effects of dissolved oxygen (0.2·10–3–9.4·10–3 mol/dm3, sulfur dioxide (0.3·10–1–2.0·10–1 mol/dm3 and Ce(III) (0.2·10–3–4.8·10–3 mol/dm3) and dose rate (0.26·1019–1.0·1019 eV/dm3·s) on the radiation — chemical yield of oxygen consumption G(–O2) and accumulation of sulfate G(HSO
), have been investigated. The reaction proceeds with G(–O2) reaching 102–103 molecule/100eV in a catalytic regime. The reaction rate in perchloric acid medium is 3–4 times lower than that in the sulfuric acid medium and depends on the SO2, O2 and Ce(III) concentrations, the reaction order varying from 1.0 to 0 and/or in the reverse direction. The mechanism of the process involves chain propagation with 3 stages and 3 intermediates: SO3H, HSO5 and Ce(IV). The catalytic effect is caused by the interaction of HSO4 with Ce(IV) ions followed by their reduction when interacting with SO2, yielding SO3H radicals. Chain termination may be due to one or two of the three intermediates or due to all three particles, the kinetics depending on this. Kinetic equations describing the experimental data have been obtained.