In this research, paleoecology of Baghmashah Formation in Rizu section based on calcareous nannoplanktons has been investigated. Baghmashah Formation is part of the Mago sedimentary mega sequence in the Tabas block that was located in the northern margin of the Neotethys Ocean in Jurassic-Cretaceous. The Baghmshah Formation in this section with 270m thickness mainly includes the alternation of green marl- shale with thin interlayers of calcareous sandstone. The study of calcareous nannofossils and index species of nannofossil indicates Berriasian- early Huterivian age for the Baghmashah Formation in this section. Investigation of the abundance of calcareous nannofossils in the studied section shows that the sedimentary basin of Baghmashah Formation in Rizu section located in low latitude with warm surface waters, and formation deposited in oligotrophic conditions with shallow environment