The Nuoergong Group, a suite of low-grade metamorphic strata composed mainly of quartzite, leucoleptite, carbonate and clastic rocks, was traditionally considered overlying directly the metamorphic basement named "Alxa Group" in eastern Alxa Block. Its formation age was identified as Changchengian based on regional stratigraphic correlation and stromatolites fossils. In order to precisely constrain the stratigraphic time, the authors present LA-MC-ICP-MS zircon U-Pb dating results for samples of three quartzite bodies from the lower Nuoergong Group. These zircon ages are mainly concentrated in the 2 530~2 500 Ma and 1 950~1 850 Ma, while a few zircons have ~1.69 Ga, ~2.0 Ga, ~2.15 Ga, ~2.35 Ga, ~2.7 Ga and ~3.4 Ga ages. The youngest zircon grain of 1.69 Ga indicates that the lower Nuoergong Group was accumulated after ~1.69 Ga. In combination with previously obtained ages of overlying strata, the authors have reached the conclusion that the deposition age of Nuoergong Group is between 1.69 Ga and 1.29 Ga and there exist the Meso-proterozoic strata in Alxa Block. The most prominent ~2.5 Ga and ~1.95 Ga age peaks suggest its affinity with the North China Craton. Therefore, it is held that they have similar tectonic environments and the Alxa Block was a part of North China Craton from Archean to Mesoproterozoic.