Kinetics and mechanism of oxidation of three methylpentoses, namelyD-fucose,L-fucose andL-rhamnose with sodiumN-chlorobenzene-sulphonamide (chloramine-B or CAB) in alkaline medium were studied at 313 K. The rate law, rate =k[CAB][S][HO−] was observed. Benzenesulphonamide and chloride ions, the reduced products of the oxidant had no effect on the reaction rate. The rate increased with increase in ionic strength of the medium and the dielectric effect was negative. Proton inventory studies were made in H2O-D2O mixtures. HPLC analysis of products indicated a mixture of aldonic acids in varying proportions. A mechanism involving the furanosidic ringform of methylpentoses which preferentially reacts with CAB in the rate limiting step is suggested.