Koyunagili coalfield in the Beypazari basin of the Central Anatolia was investigated and coal ranks were determined using fuzzy Mamdani model based on ASTM coal rank classification. This is a pilot study to investigate the applicability of the fuzzy model to determine the ranking of any coal seam. The Koyunagili coalfield, which is located at the southern part of the Beypazari basin, consists of the late Miocene coal seam within the tuffaceous rocks. The mineable coal seam is split by a 0.5-0.55 m thick clayey limestone into the upper (1.2-1.3 m thick) and lower (0.4 m thick) benches. A total of 28 profile coal samples from underground mines were collected. The samples have an average of 30.9% moisture (as-received), 23% ash yield, and 2.9% total sulphur and 4167 kcal/kg gross calorific value on an air-dried basis. Mean random reflectance values of huminite have an average of 0.34%, and show no differences across the coalfield. Coal ranking has been determined by the fuzzy Mamdani model. During processing, fixed carbon content (FCC), volatile matter values (VMV), calorific value (CV), and vitrinite/huminite reflectance (Ro %) parameters are inputs, and a total of 10 rules are used for the model. Modeling results are consistent with the previous studies.