Over 250 bird species have been listed as victims of the Shiny Cowbird (Molothrus bonariensis), a well-known obligate brood parasite. Five of the nine species of Phacellodomus (thornbirds) have been listed as victims, but none has been reported rearing cowbird fledglings. I report observations of a pair of Orange-breasted Thornbirds (Phacellodomus ferrugineigula) rearing two fledgling Shiny Cowbirds in southern Brazil. These data add a new host for the Shiny Cowbird and constitute the first report of a species of the genus Phacellodomus as an effective host of cowbirds.