A mid-Tertiary rock sequence at the Tieersihabahe locality from the Ulungur River area in the northern Junggar Basin, Xinjiang Province, China, is described. The study introduces three late Oligocene/Early Miocene faunas from the continuous section of the “Ulunguhe” and Suosuoquan formations within the sequence, and discusses the age determination, faunal correlation, and existing problems concerning the formations and faunas. The “Ulunguhe” fauna at the Tieersihabahe locality is late Oligocene in age, correlative to the Taben Buluk fauna. The 99005 fauna is probably Oligocene–Miocene transitional. The Suosuoquan fauna is regarded as early Miocene, so the Oligocene/Miocene boundary would be contained in the continuous section at the Tieersihabahe section.