Infanticide, the killing of dependent offspring, often provides direct or indirect fitness benefits to the perpetrator. Infanticide in socially monogamous systems, like that in many passerine birds, is typically performed by males in an attempt to gain access to potential mates. We observed infanticide by a female Barn Swallow (Hirundo rustica) in North America and, to the best of our knowledge, this is the first documentation of this behavior. A female pecked and threw out nestlings belonging to a neighboring pair of swallows. There were no obvious fitness benefits gained by this female, thus established evolutionary explanations are not applicable. Further investigations into the frequency of female infanticide, easily mistaken for predation, should be pursued to better assess the selective pressures driving this behavior.