The effect of electron beam irradiation on the microstructure of cellulose has been investigated using positron annihilation lifetime spectroscopy (PALS) and electron paramagnetic resonance (EPR) Spectroscopy. PALS studies of irradiated cellulose samples showed that ortho-positronium (o-Ps) lifetime increases with an increase in dose up to 80 kGy and decreases at higher doses. The EPR signal of the irradiated cellulose matrix showed the presence of multiple radical sites. These results are discussed on the basis of chemical and physical changes occurring at the microscopic level in the cellulose due to irradiation.