An antenna structure of reduced size but operating at multiple frequencies, applied to an electronic device, includes a housing, a system ground plane, and a first feed point. The housing has at least one portion made of metal material and defines a first gap and a second gap. The housing between the first gap and the second gap forms a first radiation portion. The system ground plane is positioned in the housing and defines a first slit. The first slit corresponds to the first radiation portion and communicates with the second gap. The first feed point is positioned on the first radiation portion and is electrically connected to a first feed source for feeding current and signal to the first radiation portion.