Small mammals (insectivores, bats and rodents) are one of the most useful tools to reconstruct Quaternary environment. Recent studies have demonstrated the relation between the stable oxygen isotopes (mainly δ18O) from biogenetic phosphates from rodent teeth with the δ18O from meteoric water; that at the same time can be potentially related with palaeotemperatures. This work explores the palaeoenvironment reconstructions based on the δ18O composition of phosphates from enamel of rodent teeth (mainly Murinae and Arvicolinae) to approach to the Marine Isotope Stage 3 (ca. 60-30 ka) in Northeastern Iberia. Fourteen new δ18O analyses from current samples are presented, complemented with forty-six δ18O analyses previously published. We propose methodological basis to approach to small mammals assemblages through δ18O analysis in Iberia, territory with unique environmental conditions related to its geographical location, orography and peninsula character. This methodology is test on Xaragalls cave (Vimbodí-Poblet, Tarragona), a paleontological site from MIS3, with an abundant small mammals assemblage, where fifty-one δ18O analyses have been performed on Apodemus sylvaticus incisors. The results denote a global stable climatic period in coherence with previous studies, but this work underlines climatic instability on levels C7, C6 and C4, in comparison with levels C8 and C5, more temperate. It is concluded that the δ18O analyses approach allows us to increase our knowledge about the palaeoecology of MIS3 paleontological and archeological sites from Iberia and complement other methods based on small mammal’s faunas, introducing aspects such as climatic instability events, aridity or seasonality of the accumulations.