Abstract: A board-to-board connector assembly includes a first connector (100) having a first housing (10) defining two opposite first longitudinal peripheral walls (11a) and two opposite first transverse peripheral walls (11b) connecting the first longitudinal walls. A rib (114) and a locking portion (116) are respectively defined in corresponding inner wall of the first longitudinal and transverse peripheral walls. A second connector (200) comprises a second housing (30), a plurality of terminals (40) received in the second housing and a pair of metal ears (50) engaged with two opposite second peripheral walls. The terminal and the metal ear respectively define a protrusion (431) and a projection (54) extending outward thereof and snugly fit against the corresponding rib and the locking portion when the first and second connectors engage with each other.