The kinetics of oxidation of D-mannose with pyridinium chlorochromate, C₅H₅NHCrO₃Cl, was investigated in aqueous perchloric acid medium. The ionic strength of the medium was maintained constant by adding sodium perchlorate solution. The oxidation process exhibits unit dependence in each of the reactants, namely D-mannose and pyridinium chlorochromate. The reaction is acid catalyzed. A 32 stoichiometry is observed in the oxidation and the reaction did not induce polymerization of acrylonitrile. Activation parameters have been computed by measuring the rates at different temperatures. A reaction mechanism consistent with the experimental observation is proposed.