The kinetic investigation in Ru (III) catalysed oxidation of lactose by chloramine T in acidic medium has been done in the temperature range 30⁰- 50⁰ C. The reaction is carried out in the presence of mercuric acetate as a scavenger for Cl^- ion. The reaction has a first order dependence on chloramine T as well as on Ru(III) and Zero order of the reaction with respect to substrate. Positive effect of [Cl^-] was observed in the oxidation of lactose. An increase in the rate of reaction with the decrease in Hg(OAc)₂ was observed for the redox system. The rate of oxidation is unaffected by the change in the ionic strength (µ) of the medium. The oxidation product of the reaction was identified as Lactobionic acid, was analysed through spot and spectroscopic studies respectively. On the basis of kinetic results and product analysis a probable mechanism were suggested.