A power line Ethernet adaptor is suitable to be applied to an external module including a first connector. The power line Ethernet adaptor includes a housing, a cover and a circuit board. The housing has an accommodating space. The cover is movably connected to the housing to move between an on-position and an off-position. When placed at the off-position, the cover covers the accommodating space. The circuit board is disposed in the accommodating space and has a power line Ethernet module and a second connector. When at least a part of the external module is disposed in the accommodating space, the first connector and the second connector are electrically connected to each other to establish the signal connection between the external module and the power line Ethernet module, and the cover also covers the external module when placed at the off-position.