This paper reports the first record of Eumops underwoodi in the Baja California peninsula. This record expands the species' distributional range in Mexico along the peninsula. We propose 2 plausible biogeographical explanations. First, the species has the ability to travel across the Gulf of California from the coast of Sonora to the eastern side of the Baja California peninsula and there establish. Second, there is a continuous distribution of the species throughout the mountain ranges that run longitudinally along the Baja California peninsula from the United States border down to the southern tip. We collected one male specimen of E. underwoodi in xeric-riparian habitat. We suggest a continuous distribution pattern of this species along the cliffs in the Baja California peninsula.