Thinlayered and laminated tuff was developed in the Wulalike Formation in the northwestern Ordos Basin.This tuff bed was produced by volcanic ashfall deposits which can reclassify the Ordovician stratigraphic framework of Ordos Basin and provide importantconstrains on the plate tectonic setting of the northwestern Ordos Basin as well as major volcanism—magma activities. In this contribution，wecarried SHRIMP UPb dating and Hf isotope on tuff sample collected from Zhuozishan area, located in Wuhai City，Inner Mongolia.LAICPMS UPb dating on zircons has yielded a weighted average of 4549±34Ma（MSWD=002）. SHRIMP UPb dating on zircons from the tuff sample has yielded a set of concordant ages of 4332±33～4642±35Ma with the mean age 4564±42Ma（MSWD=19）. Accordingly,the main depositional period of Wulalike Formation，which is still controversial，is redefined to Darriwilian—Sandbian，Middle—Late Ordovician. In situ zircon isotope analysis yieldedεHf(t) = +402 ~ +1098,n(176Hf)/n(177Hf)ratios of 0282 619~0282 806 and twostage model age of 729~1178Ma. According to their regional distribution, it is thought that these tuffs derive from volcanic eruption in the North Qinling or/ and North Qilian region. The zircon age and magmas source are in accordance with the tuffs from Wuhai city to the tuffs(or Kbentonites) from the southwestern Ordos Basin, which means all the western and southern Ordos Basin affected by the North Qilian or/ and North Qinling Early Paleozoic orogenic belt during Middle—Late Ordovician.