A lateral engagement structure for an electrical connector capable of engaging with a lateral side of a circuit board includes a main body and an elastic arm. The body includes vertical and horizontal plates, wherein a first stopper block is set at a middle of a front end of the vertical plate, and a space is formed below the first stopper block. The arm has a rear end connected to the body, a free front end, and a front section having an actuator and an engagement portion engaged with the board. The arm's front end is bent toward the first stopper block to form a first transversal plate. When the arm is elastically moved toward the vertical plate, the first transversal plate is stopped at the first stopper block, and the engagement portion still engages with the board. When the first transversal plate passes through the space, the engagement portion is caused to separate from the board.