Radicals and radical ions formed on γ-radiolysis of aromatic carboxylic acids containing a thioether group in the polycrystalline state at 77K and on subsequent warming over the temperature range of 95–293K were identified using the electron spin resonance technique. In all carboxylic acids studied, monomeric sulfur radical cations (X-S + -Y-COOH) and radical anions formed by an addition of an electron to the carboxyl group (X-S-Y-COOH) − were detected at 95K. On further warming over the 150–293K range various S-centered radicals (XS) and C-centered radicals were observed. The results are discussed in terms of the following competitive reaction pathways: fragmentation, decarboxylation, and deprotonation of the parental monomeric sulfur radical cations. Carbon dioxide was identified and quantified (G=0.2–3.5) in all carboxylic acids exposed to γ-radiation.