The Jahrum Formation, at Kuh-e Gach, (Lar area) have been investigated in order to determine its biostratigraphy and palaeoecology. The Jahrum Formation with the total thickness of 404 m is conformably overlies the Sachun Formation and is overlain by Limestone of the Asmari Formation. Larger foraminifera are the main means for the biostratigraphic zonation of carbonate sediments. Based on study of foraminifera, four assemblages zone were identified. The distribution of the larger benthic foraminifera indicates that shallow marine carbonate sediments of the Jhrum Formation at the study area have been deposited during the Late Paleocene-Eocene. The restricted and hypersaline lagoon facies is characterized by various taxa of imperforate foraminifera. The shallow open marine with normal salinity is dominated by thin and flat Operculina. The most common skeletal components in limestones of the Jahrum Formation are large benthicforaminifera,whereas bryozoan,corallinacean algae, echinoid and gastropod components are less common.