The radiation-induced graft copolymerization of styrene to cellulose has been studied in vacuo at 30°C and at dose rates from (0.37 to 8.73) × 10−2 W/kg. Dioxan was used as solvent for monomer and polystyrene homopolymer, and water (2% total volume) was incorporated as swelling agent for cellulose. The concentration of styrene in the bulk medium was varied from 0.432 to 3.46 moles/l., and the rates of both grafting and homopolymerization were shown to be proportional to [monomer] · [intensity]1/2. The value of 3.3 × 10−4 l. mole−1 sec−1 derived for kp2/kt in homopolymerization is similar to that for normal free-radical polymerization of styrene. However, reduced termination during grafting yielded a much higher value (58 l. moles−1 sec−1). Degradation of cellulose in the absence of monomer was followed viscometrically, and values of 13.5 and 24.6 were derived for G (scission) in vacuo and in air, respectively.