A tether anchorage device for a swivel seat of a vehicle is provided. The device is configured such that an anchor including a horizontal bar and a vertical bar is mounted on a rear surface of the swivel seat, and a tether belt for fixing a baby seat is anchored to the anchor while being bound in a vertical direction as well as a horizontal direction of the swivel seat, so that the baby seat may be securely fixed to the swivel seat regardless of a rotating position of the swivel seat.