The small-sized Astrohippus stockii was a one-toed horse restricted to the latest Hemphillian (Hh4) NALMA (5.8–4.6 Ma). Although this species is relatively common in fossil localities of the United States and Mexico, much remains to be known regarding its feeding ecology. We applied a multidisciplinary approach to reconstruct the dietary behavior of A. stockii based on a sample from Arroyo La Carreta locality, latest Hemphillian of Guanajuato, central Mexico. Carbon isotope and meso- and microwear analyses were conducted. The δ¹³C isotope data indicate a diet consisting of both C3/C4 plants with a preference for C4 plants (average δ¹³C of -1.9‰ ± 1,3‰ [SD]), whereas the micro-(high number of scratches and a low number of pits) and mesowear (round to blunt cusps and low relief) signatures implied processing of abrasive sources (biogenic and abiogenic). The information about the feeding ecology of A. stockii from Guanajuato, Chihuahua, Florida and Texas showed that this North American horse had broad feeding habits, ranging from almost exclusive grazing to browsing. The dietary flexibility in this horse species is probably related to local environmental conditions, suggesting an adaptable dietary regime across its geographic distribution. This is the first study that uses three of the most widely applied analyses to reconstruct the feeding ecology of a Mexican fossil ungulate species.