The title complex, [Na(C₈H₉O₅S)]_n, is polymeric and consists of broad layers parallel to (100) made up of an inner hydrophilic core of Na⁺ cations and polar SO₃C(OH). groups, padded on both sides by two hydrophobic layers of pendant methoxyphenyl groups. The Na⁺ cations in the inner core are six-coordinated into highly distorted NaO₆ octahedra by four symmetry-related (hydroxy)(4-methoxyphenyl)methanesulfonate anions, leading to a tightly woven two-dimensional structure. While there are some hydrogen bonds providing interplanar cohesion, interactions between adjacent layers are weak hydrophobic ones. The present compound appears to be the first reported structure containing the (hydroxy)(4-methoxyphenyl)methanesulfonate ligand.