By using organic non-woven fabrics, which are less costly than inorganic ones, we have studied the effect of the fabrics attached to a conventional polyethylene (PE)-based separator on sedimentation of sulfuric acid to prevent stratification in flood-type lead-acid batteries. The effect of surface treatment for the fabrics on the diffusion of sulfate ions has also been studied to reduce the electric resistance. The results of model experiments showed that the organic non-woven fabrics suppressed the sedimentation of sulfuric acid. In addition, by clarifying the relationship between surface tension of non-woven fabrics and diffusion coefficients of sulfate ions, we found that hydrophilic non-woven fabric with a SiO2 overcoat film was the most effective for improving the diffusion of sulfate ions.