Electron beam irradiation (EBI) was used to improve the reactivity of bamboo dissolving pulp. An EBI treatment with a dose lower than 10 kGy showed that the Fock reactivity of the dissolving pulp noticeably increased from 69.5% to 98.3% with negligible cellulose losses. However, when the irradiation dose was higher than 10 kGy, the Fock reactivity increased with an observable α-cellulose loss, which could result in the lower strength of end-products. The gradual increase of Fock reactivity has a good agreement with the reduction of the degree of polymerization (DP) of cellulose. This suggests that lowering the DP of cellulose could enhance cellulose reactivity. Later analyses confirmed that an EBI treatment creates fiber pores that facilitate a cellulose xanthation reaction. The EBI treatment could randomly destroy cellulose crystalline and amorphous regions. The results indicated that the reactivity improvement was due not only to the DP, but also due to the changes in the fiber morphology and cellulose structure caused by the EBI processing.