A defected ground structure with shielding effect is provided. The structure includes a dielectric layer, a defected metal layer, a grounded metal layer and at least a conductive mushroom-like structure. The defected metal layer has a line-shaped opening and is disposed in the dielectric layer. The conductive mushroom-like structure is disposed between the defected metal layer and the grounded metal layer and is arranged along an extending direction of the line-shaped opening periodically. The conductive mushroom-like structure includes a fungating part and a stipe part. The fungating part is parallel to the defected metal layer and a distance is maintained away from the defected metal layer. The projection area of the fungating part on the defected metal layer covers a length of the line-shaped opening corresponding to the fungating part. The stipe part connects the fungating part and the grounded metal layer.