Characterization of the pore structure in cellulose beads is difficult since the pores vary in size, shape and orientation. In this work pore sizes in cellulose beads have been estimated from self-diffusion measurements using the spin echo NMR technique. Structures were identified by measuring the apparent diffusion coefficient at different diffusion times. The technique was tested using liquid diffusion between glass beads. The resulting void sizes show good agreement with theoretical predictions. Estimates of the pore sizes in dry cellulose beads of different porosity are found to be in agreement with results from the mercury intrusion technique. It is concluded that diffusion studies using the spin echo NMR technique represent an alternative technique to characterize pore sizes in cellulose beads.