An antenna device for a portable terminal, a portable terminal, and a method for providing an antenna device in a portable terminal are provided. The antenna device includes a radio frequency (RF) board on the portable terminal, an antenna connected to the RF board, a connection line for connecting the RF board to the antenna device, and matching circuits at both ends of the connection line. The matching circuits compensate for loss from the connection line itself and connection losses so that a signal can be adjusted in accordance with the properties of the antenna. Consequently, the properties of the antenna device are stabilized.