The homogeneous grafting of N-vinylpyrrolidone (NVP) onto cellulose was carried out in a dimethyl sulfoxide/paraformaldehyde (DMSO/PF) solvent system. The diffusive permeabilities of solutes through the NVP-grafted cellulose membranes, apparent activation energy for solute permeation through them, states of water in them, and their microphase-separated structures were investigated. The solute permeability through the grafted membranes was superior to that through the cellulose membrane cast from the DMSO/PF solution of cellulose. The total water and nonfreezing water contents of the grafted membranes were larger than those of the cellulose membrane. The difference in permeability through the membranes was not correlated quantitatively with the amount of each state of water in them. Activation energies for permeation of solutes through the grafted membranes were similar to those through the cellulose membrane.