The reaction in aqueous solution between carbonyl sulfide (COS) and the polyamines ethylenediamine and diethylenetriamine has been studied experimentally using a conductimetric stopped-flow technique. The experimental results indicate that this reaction follows a zwitterion intermediate mechanism leading to: [GRAPHICS] Values of the rate constants k2, k(Am) and k(w) at 298 K are reported for both ethylenediamine and diethylenetriamine. Activation energies for k2, k(Am) and k(w) are also reported for diethylenetriamine.