The study of the terraces and its associated faunas from the areas of Toledo and Fuentidueña de Tajo in the Valley of the Tagus River, mainly from a palaeoenvironmental point of view, has been made in this work. Six new sites of fossil microvertebrates and fossil molluscs were found when this work was undertaked. Many of the sites with remains of microvertebrates and all the sites with fossil mollucs that were found in that prospecting are presented for the first time in this work. As regards to the last, it can be remarked that all the shells of the molluscs find out are of a very small size. That could be the consequence of the alloctone origin as it happens in the seasonal river side flooding. This suggestion is supported by the presence of freshwater and terrestrial species mixed in the same sample, as, for example, Succinea putris (characteristic biotope of humid areas near the river side), together with Helicella madritensis with a terrestrial habitat. The conditions of life of the twelve species of mollucs here analyzed suggest a temperate climate in the Middle Pleistocene at the time of the sites deposition, similar to the present day in the area. Besides, the presence of Helicella madritensis, a xerophillus species that lives today in the arid areas of the central plateau of the Iberian Peninsula, suggests a climate with large dry periods not very different from now. The habitat of Truncatellina cylindrica (very dry calcareous grassy or rocky places) and that of Vallonia costata (dry open calcareous places) supports the sames suggestions.Peer reviewed