In this research, the biostratigraphy, microfacies, and depositional environment of carbonate sediments of the Jahrum Formation will be investigated based on microscopic textures and the distribution of benthic foraminifera. The Jahrum Formation was measured from Kuh-e-Hamze Ali in the Chaharmahal Bakhtiari province (Zagros Basin, Iran). The biostratigraphic analysis of this formation has led to the detection of three biozones in this area. These biozones consist of Somalina subzone, Nummulites–Alveolina assemblage subzone, and Nummulites fabianii- Nummulites striatus assemblage subzone which assigned to Middle and Late Eocene. The Nummulites fabianii- Nummulites striatus assemblage subzone is represented for the first time in the studied area. Nine microfacies are identified based on their fossil content (mainly foraminifera) and sedimentary textures. They consist of Dolostone, Mudstone with quartz, Bioclast- miliolids wackestone/packstone, Praerhapydionina -miliolid wackestone, Alveolina -Nummulites-Orbitolites wackestone/packstone, Bioclast–miliolid-Rotalia wackestone/packstone, Bioclast-lump packstone/grainstone, Interaclast-bioclast-Alveolina wackestone/grainstone, and Bioclast-Nummulites wackestone/packstone. These facies were deposited in four major depositional environments from a tidal flat, lagoon, shoal, and open marine environmental settings. The depositional environment of the Jahrum Formation is interpreted as a carbonate ramp. Manuscript profile