Abstract: An electromagnetic shielding element and, transmission line assembly and electronic structure package using the same are provided. The electromagnetic shielding element is applied to the transmission line assembly and the electronic structure package to shield electromagnetic noise. The electromagnetic shielding element includes a quantum well structure, and the quantum well structure includes at least two barrier layers and at least one carrier confined layer located between the two barrier layers. Each barrier layer has a thickness between 0.1 nm and 500 nm, and the thickness of the carrier confined layer is between 0.1 nm and 500 nm. The electromagnetic shielding element absorbs electromagnetic wave noise to suppress electromagnetic interference.