The Tsetserleg terrane forms part of the Hangay-Hentey basin of Mongolia, which in turn forms part of the Central Asian Orogenic Belt. Whole-rock major and trace elements compositions of 94 Devonian and Carboniferous sandstones and mudrocks (siltstones and mudstones) from the Tsetserleg terrane were determined by X-ray fluorescence spectrometry. Analyses are reported for the Devonian Erdenetsogt (n = 54) and Tsetserleg Formations (n = 26), and the Carboniferous Jargalant Formation (n = 14). The main feature of the data is the relatively uniform average SiO2 content of the sandstones in each formation. Average SiO2 contents in the mudrocks are equally uniform, and are only slightly less than those for companion sandstones. Consequently, average concentrations of most of the other elements analyzed are only slightly greater in the mudrocks than in the sandstones. These features reflect the textural and mineralogical immaturity of these sediments, which are classed as wackes and shales based on geochemical parameters.13;