The Oligo-Miocene carbonates of the Qum Formation in the Alborz wells (Alborz anticline), Central Basin, are oil and gas producing fractured reservoirs. Depositional environments of the Qum Formation, in the studied area, have been reconstructed by a detailed petrographic analysis of microfacies (MF). This approach reveals a vertical sequence of ten microfacies designated by numbers 1-10. Based on the petrographic characteristics and environmental significance the studied MF were interpreted in terms of depositional environments as follows: pelagic wackestone, MF-1 (basin); large-foram bearing wackestone-packstone, MF-2 (distal talus); algal bryozoan packstone-grainstone or floatstone, MF-3 (proximal talus); algal bryozoan floatstone-roudstone or framestone, MF-4 (reef); miliolid and gastropod bearing packstone-grainstone, MF-5 (restricted shelf); ooid grainstone, MF-6 (oolitic shoal); miliolid and gastropod bearing bioclastic wackestone, MF-7 (shelf lagoon); sandy limestone and sandstone, MF-8&9 (intertidal) & anhydrite, MF-10 (supratidal). A carbonate ramp is envisaged for deposition of this formation in the Qum Basin.