A spinnable, isotropic solution containing cellulose, phosphoric acid and/or anhydrides of phosphoric acid and water is prepared by dissolving cellulose in a solvent, the solvent being a homogeneous mixture of water and at least one of phosphoric acid and anhydrides of phosphoric acid such that the solvent contains 72-85 wt. % of phosphorous pentoxide, P.sub.2 O.sub.5. The cellulose is mixed with the solvent in a mixing apparatus, the mixing apparatus having mixers, kneaders or the like, and capable of generating high shearing forces. The solution is converted from anisotropic phase to isotropic phase by the addition of water. The water required to convert the solution to the isotropic phase is added either just prior to, during or after the mixing step. The solvent preferably contains 72-80 wt. % P.sub.2 O.sub.5 and 7-20 wt. % of cellulose, and is used to make hollow fibers, membranes, non-woven films, and other articles requiring the use of cellulose-containing solutions.