Microtomarctus is an extinct monospecific genus of the Borophaginae subfamily of canids native to North America. It lived during the Early to Middle Miocene, and existed for approximately . Fossil specimens have been found in Nebraska, coastal southeast Texas, California, New Mexico, Nevada, and Colorado. It was an intermediate-size canid, and more predaceous than earlier borophagines.
Like some other borophagines it had powerful, bone-crushing jaws and teeth.