The kinetics of the oxidation of 1-butanethiol and 2-butanethiol by hexacyanoferrate (III) ion in methanol-water medium and in presence of hydroxyl ions have been studied. The reactions show a first order dependence on hexacyanoferrate (III) ion and a zero order in thiol when great excess is used (15–60 times). In the oxidation of 1-butanethiol (1-BT), the order in hydroxyl ions shows a transition from zero towards unity whereas in the case of 2-BT, the first order rate constant increases linearly with increasing hydroxyl ion concentration. The reaction follows second order kinetics at low concentrations of thiol (ca. <6.0 × 10−3M), and the second order rate constant decreases with increasing thiol concentration. The kinetic data indicate that the accumulation of hexacyanoferrate (II) ions is responsible for the change of kinetics. This possibility has been further explored, and the results are presented in Part II of the present communication. The rate increases with increasing ionic strength, and dielectric constant of the medium. Activation parameters have been evaluated and discussed on the basis of kinetic and steric effects.