This study investigates the petrographic analysis, microlithotype, and palaeoenviroment of deposition of the upper Triassic Olang coal deposits in northeastern Iran. The average maceral composition of the studied coals consisted of 82.3, 8.9, 0.4 (vol.%), vitrinite, inertinite and liptinite groups, respectively. Vitrinite macerals include equal portions of collotelinite and; collodetrinite and a small quantity of corpogelinite also is present in all coal seams. Semifusinite and fusinite are the most abundant inertinite macerals. The Ground Water Index (GWI) suggests that these coal seams have evolved in a limnic coal fades (a bog palaeomire system) under ombrotrophic hydrological conditions, except the K(6)G coal seam, which evolved a limnic coal facies (a bog palaeomire system) under mesotrophic hydrological conditions. The Vegetation Index (VI) values are indicative of the dominance of herbaceous plants in the formation of coal seams of the Olang area. (C) 2012 Elsevier B.V. All rights reserved.