Abstract: This paper reports the first occurrence of Tertiary mammalian fossil, an anthracothere lower premolar, from an oil well core at depth of 1739 m of the drill Fa-24 in Liaohe Oilfield, which situates about 37.5 km west to the city of Shenyang (Mukden), Liaoning Province. The specimen came from the upper part of Member 3 of Shahejie Formation, a set of grey silty mudstone and pelitic siltstone. The premolar, probably Pa, is tentatively ascribed to Anthracotheriidae gen. et sp. indet.