Abstract: A new species of Leptarctus is described on the basis of a well— preserved skull from the North American Miocene. Leptarctus is only known from the Miocene of Nei Mongol (Inner Mongolia) and North America. The new specimen differs from other species in having an unusually enlarged upper dentition and a hooked process on the tympanic bullae. The third upper incisors are caniniform and are curved toward the canine. The dental characters of this new species indicate it had omnivorous diet.