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Gellan gum undergoes gelation by forming domains composed of associated double helices. Here the further random aggregation of associated double helices seems necessary for the formation of the network in the case of Na-gellan with adding NaCl. Gellan gum aqueous solutions were prepared with or without adding various concentrations of NaCl, and their gel-sol transitions were observed by the differential scanning calorimetry (DSC) and the small-angle X-ray scattering (SAXS). The DSC endothermic peaks are attributed to the dissociation of the ordered domains, and the network dissociation in the case of gel samples. The SAXS results are analyzed in terms of the molecular models of associated double helices.