The crystal structure of the title compound, [Na(C36H61O11)]·2H2O, was first reported by Duax et al. [J. Am. Chem. Soc. (1980), 102, 6725–6729]. We report here the crystal structure of a new polymorph, determined at the low temperature of 180 (2) K, in the same orthorhombic non-centrosymmetric space group P212121. The structure contains one crystallographically unique sodium monensin complex, showing a highly distorted octahedral coordination environment for Na+, forming undulating layers in the ac plane. H atoms from the pendant hydroxyl groups involved in head-to-tail hydrogen bonding with the carboxyl­ate group and from the crystallization water mol­ecules occupying the interlayer spaces have been successfully located in difference Fourier maps.