The kinetics of oxidation of thiosemicarbazide (TSC) in aqueous perchloric and sulphuric acid media, and also that of thiocarbohydrazide (TCH), its metal complex and its hydrazone in perchloric acid medium, by hydrogen peroxide have been investigated under varying conditions. The rates show first order kinetics each in [oxidant] and [substrate] in all the cases. The rate dependences in [H⁺] are different. Inverse first order kinetics in [H⁺] are observed for TCH oxidations and varying inverse orders in [H⁺] (depending upon its concentration) are seen for TSC oxidations. Effects of varying ionic strength, dielectric constant of the medium etc. have also been investigated. Mechanisms consistent with the observed results have been considered and discussed. The metal complexation of thiocarbohydrazide and its conversion into hydrazone enhance the rate of oxidations but have little effects on the kinetic orders.