Kinetics of phosphotungustic acid catalysed oxidation of aliphatic hydroxy acids such as lactic, tartaric and tartronic acids by N-chlorosuccinimide have been studied in aqueous acetic acid medium. The order of [N-chlorosuccinimide] was found to be one and fractional-order with respect to catalyst [PTA]. However, the order of [hydroxy acids] changed from unity to a fractional one in presence of PTA. The insignificant change in rate was observed with [H⁺] and neutral salts. The basis of kinetics features, the probable and activation mechanism are discussed and individual rate parameters evaluated.