The intercalation of poly(ethylene oxide) (PEO), into molybdenum disulfide, like that of other electron pair donors, leads to mixed ionic–electronic conductors. At room temperature, intercalates show electrical and lithium-ion conductivities better than MoS2 and bulk PEO composites, respectively. However, these products are known to be sensitive to temperature; indeed, in the range 80–100°C an irreversible decrease of the electrical conductivity is observed. In order to investigate these features, the thermal behavior of a series of polyethers of different molecular weights (poly(ethylene glycol) (Mw 3400) and PEO with Mw in the range 104–4×106, pure and intercalated in MoS2, (Lix(MoS2)(polyether)y with x∼0.1 and y=1.1−1.5), was comparatively analyzed. Furthermore, the effect of thermal treatment of the sample on the electrical conductivity was studied for one of the intercalated products. Results indicate that irreversible changes, detected by both loss of weight and a significant conductivity lowering, are occurring in the range from about 100°C to a temperature near to the decomposition point of the organic phase at about 350°C.