Smugglers left behind a live tiger cub in a duffel bag when they fled back to Mexico after attempting to cross the Rio Grande into Texas.
US Customs and Border Protection officials said the male tiger, believed to be three or four months old, has been placed at the Gladys Porter Zoo in Brownsville.
Border Patrol agents patrolling on Monday along the river near Brownsville saw three people trying to enter the US illegally.
An agency statement says the trio abandoned a bag and returned to Mexico.
Officers discovered the cub stuffed in the bag.
Agent Robert Rodriguez said that the tiger appeared calm and was possibly sedated.