An antenna module disposed on a substrate having a first and a second surface opposite to each other includes a microstrip line, a first radiator, a ground radiator and a ground plane. The microstrip line, the first radiator and the ground radiator are disposed on the first surface. The microstrip line includes a first and a second end opposite to each other. The first end includes a first feeding end. The first radiator is connected to the second end of the microstrip line. The ground radiator surrounds the microstrip line and the first radiator and has a first opening and two opposite grounding ends. The first end of the microstrip line is located in the first opening. A gap is formed between each grounding end and the first feeding end. The ground plane is disposed on the second surface. The ground radiator is connected to the ground plane.