⁸⁷Sr/⁸⁶Sr ratios of marine carbonate samples collected from a sedimentary section of the Late Cretaceous in the south of Tibet were measured. Based on the absence of cathodo-luminescence and a very low Mn/Sr ratio (average 0.06) of the samples, it is thought that they contain information on the original seawater strontium isotope composition. The strontium isotope evolution curve of the Late Cretaceous in Tibet we established here, is consistent with other coeval curves from Europe, North America and Antarctica, supports the notion that the strontium isotope composition of seawater is governed by global events, which provides a new approach for the inter-continental and inter-basinal correlations of Late Cretaceous in the area and is a complementarity for biostratigraphy. In addition, we attempt to determine the age of the boundaries for Campanian/Santonian and Maastrichtian/Campanian by⁸⁷Sr/⁸⁶Sr ratios for Gamba section in southern Tibet. The two boundaries are located in the thickness of 217 m (83.5 Ma) and 291 m (71.3 Ma), respectively.