In the Qoltag tectonic belt of eastern Tianshan, southwestern Central Asian Orogenic Belt, there are widespread Carboniferous marine volcanic-sedimentary successions. These successions record critical information about the development of the North Tianshan Ocean. To date, ages of them are uncertain, due to the lack of index fossils. In this study, abundant rugose corals, fusulines, and some conodonts were collected that allow us to assign precise ages for the successions. In ascending order, we recognized four rugose coral assemblages, including the Zaphrentites-Meniscophyllum Assemblage, Gangamophyllum-Palaeosmilia-Kueichouphyllum Assemblage, PetalaxisKoninckophyllum Assemblage and the Ivanovia Assemblage. Four fusuline zones, including the Profusulinella parva-Profusulinella staffellaeformis Zone, Profusulinella wangyui-Eofusulina trianguliformis Zone, Fusulinella-Fusulinella Zone and the Rauserites rossicus Zone were also established. Based on these new fossil assemblages and biozones, age of the sedimentary units in the Qoltag tectonic belt was constrained as following. The Nanbeidagou Formation ranges from Tournaisian to early Visean in age, the Yamansu Formation from early Visean to late Bashkirian, the Shaquanzi Formation from late Bashkirian to middle Moscovian, the Dikaner Formation from Bashkirian to Moscovian, and the Qi'eshan Formation from Bashkirian to as late as early Gzhelian. The updated Carboniferous framework enables the establishment of regional standard and improves the precision of correlation with others. It further provides a sound basis for the future interpretation of tectonic evolution in the southwestern Central Asian Orogenic Belt.