Several pathways leading to the decomposition of chlorite and chlorous acid have been published. In this study, both experimental and computational approaches have been applied to clarify the authenticity of the different routes. The decomposition of chlorine (III), i.e. chlorous acid and chlorite, was monitored with iodometric titration at changing chloride concentrations, temperature, and existence of iron (III) at pH 1−3. Dimethylsulfoxide (DMSO) was used to prevent hypochlorous acid from reacting with chlorite. Chlorine dioxide was not formed in the absence of metals when hypochlorous acid and chlorine were trapped. The self-decomposition of Cl(III) proceeds only via the acidic form while chlorite is stable. Chloride ions enhanced the chlorous acid decomposition rate especially at low pH. Chlorite decomposes in the presence of Fe3+ ions. General kinetic parameters and their temperature dependencies were determined for chlorous acid self-decomposition.