Black-footed ferrets typically prey upon prairie dogs at night while prairie dogs are presumably sleeping. Prairie dogs can act aggressively towards aboveground ferrets in daylight and we observed prairie dog aggression towards ferrets four times in South Dakota and Montana. Ten behaviors by prairie dogs were recorded during aggressive interactions with ferrets including chasing, blocking, and physical contact. One of the aggressive prairie dogs was confirmed as an adult male and three of four encounters occurred Jun. through Jul. Interactions lasted <10 min and neither the prairie dog nor ferret were visibly injured.