A built-in antenna of a portable terminal and a method of forming the same are provided. The built-in antenna includes a first conductor having a specific length and used for a ground, a second conductor disposed with a specific distance in parallel to the first conductor to couple with the first conductor and used for power feeding, and a separating element disposed between the first conductor and the second conductor to separate the first and second conductors. Accordingly, the built-in antenna may exhibit a smooth radiation property even if a metal construction is used in a device and thus may implement robustness improvement of the device and make the device slim and have an attractive outer appearance. In addition, a method of improving antenna efficiency may prevent deterioration of the radiation property of the antenna radiator of the related art by using simple processing, and the metal construction may be used as a radiator.