A data card includes a casing, a circuit board in the casing, a plug electrically connected with the circuit board and a cap part capable of covering the plug; wherein one end of the casing is provided with the plug; a card slot is defined in the casing at a joint of the casing and the plug, and the cap part covers a notch of the card slot when the plug is inserted into the cap part. The invention is mainly used in wireless data signal receiving or transmitting device.