Abstract: The marine Jurassic-Cretaceous boundary strata are outcropped in southern Tibet. The strata in Gyangze area are divided into Weimei and Jiabula Formations. The samples were observed and analyzed by means of polarizing light microscope (PLM) and scanning electron microscope (SEM), and the well-preserved calcareous nannofossils were found for the first time in the black shale of Jiabula Formation along the Jiabula-Gokou section. Biological abundance and diversity are relatively low in the study area. According to the fossil identification the biota discovered is mainly the Ellipsagelosphaeraceae fauna which is abundant with minor variation at the genus and species level. The nannofossils indicate that the Jiabula Formation is a product of Early Cretaceous deposition. Considering the coexistent fossils of ammonites and bivalves, the authors hold that the age of Jiabula Formation is the Berriasian-Valanginian of Early Cretaceous. The significant finding shows that the Early Cretaceous nannofossils occur in the eastern Tethys. The discovery of nannofossils provides new evidence for the age of marine strata and their stratigrphic correlation, and also indicates the possibility of the marine Jurassic-Cretaceous boundary study.