An electrical connector assembly (1) includes a card edge connector (20) used to be mounted on a mother board (10) and defining a slot (210), a daughter card (30), and a board hold down (40) for being mounted on the mother board. The daughter card includes a mating edge (31) inserted into the slot of the card edge connector, and a rear edge (32) opposite to the mating edge and defining an engaging hole (320). The board hold down is separated from the card edge connector and includes a pivot bracket (42) engaged with the engaging hole of the daughter card, and a pin latch (44) pivoted on the pivot bracket and having a latch portion (442) abutting against the rear edge of the daughter card for preventing the rear edge from rising upwardly.