In relation to the graft copolymerization of cellulose using Ce4+as catalyst，the me-chanism of eellulose oxidation and the reaction sites on the cellulose macromolecular chain in Ce4+-H2O-cellulose system were studied．From the experimental data concerning the rate of reduction of Ce4+ to Ce3+ in aqueous solution，the photosensitive character of this system has been confirmed．From the rates of oxidation of eellulose and its related model compounds，such as hydrocellulose，cellobiose，dialdehydeceIlulose，glucose and methylglucoside，as determined in eerie salt solution，the kinetics of cellulose oxidation may be represented bv the fol- lowing equation：where [I]0，[II]0 and [III]0 are the initial concentrations of the functional groups of type I，II and III，and kI，kII and kIII are their reaction rate constants respectively．By determining and comparing the rate constants of the same type but of different cellulose model compounds，it was found that the values of k for the same functional group are approximately equal irrespective of the model compounds to which the particular type of functional group is attached．It was also confirmed that there are at least three oxidation sites on a cellulose macfomolecular chain．The sites of greater and medium reactivity are the aldehyde group and 5

6-glycol unit of the terminal anhydroglucose unit respectively．The least reactive site is the hydroxyl groups attached to the third position of the rest of anhydroglucose rings．Though the value of kIII is very small，nevertheless，the reaction of third position should not be neglected for the number of such hydroxyl groups is great． When cellulose is oxidized by ceric salt，it was found that one mole of terminal aldehyde group or 5，6-glycol unit consumes two moles of eerie salt and was finally con-verted into new aldehyde group．Cellulose free radical formed as an intermediate pro-duct initiates the graft copolymerization．Hence，it may be assumed that the copolymer of cellulose obtained by Ce4+ initiation is possibly a graft-block complex copolymer.