Abstract: The emphasis is placed upon the examination of the major elements, trace elements and REEs in the mudstone and approaches to the provenance and weathering in the Middle Jurassic Shaximiao Formation, Zigong, Sichuan. The study of major elements and REEs shows that the detritus are derived mostly from the felsic rocks in the source areas. The CIA (chemical index of alteration) and ICV (index of chemical variation) indexes suggest a low to moderate chemical weathering, implying that the study area was once in the semi-arid palaeoclimatic conditions during the Middle Jurassic.