ABSTRACT: The Indo-Burmamountain range represents an accretionary wedge which resulted from subduction of the Indian plate beneath the Eurasian plate. It is situated between the eastern Himalayan Namche Barwa syntaxis and the Sumatra–Andaman subduction zone.The rocks exposed in the Mizo Hills form a part of the Indo-Burma range. Although the geology of theMizo Hills has been studied for decades, fundamental aspects of age and paleoenvironment remain debatable. In this study, calcareous nannofossils have been used for refining the biostratigraphy and paleoenvironment of the Upper Bhuban Formation (UBF) of a part of Mizoram. A calcareous nannofossil assemblage comprising eleven species of eight genera have been recognized. Though the nannofossil yield is poor with a moderate to low preservation, their study is significant in determination of age and paleoenvironment. By integrating the calcareous nannofossil and known foraminiferal assemblage data, we constrain the studied succession to Calcareous Nannofossil Zone CNM7 of Backman et al. 2012 which is equivalent to early part of the middle Miocene. The relatively good abundance of Helicosphaera, presence of Discoasters and the published foraminiferal data indicate hemipelagic depositional setting for the UBF in Mizoram.