Abstract: There exist several depositional breaks and unconformities in the Mesoproterozoic successions in the Yanliao rift trough. The examination of the attributes of the unconformities in this study is based on the field investigation, geological characteristics and stratigraphic correlation. The unconformities at the bottom of the Dahongyu, Gaoyuzhuang and Yangzhuang Formations are interpreted to be of sedimentary origin. On the whole, the unconformities at the bottom of the Dahongyu Formation resulted from the transgressive onlap; those at the bottom of the Gaoyuzhuang and Yangzhuang Formations are attributed to the eustatic fluctuations, and those at the top of the Tieling and Xiamaling Formations are caused by the large-scale tectonic uplift and thus have a tectonic origin.