An electrical connection box includes an outer box and an inner box to be accommodated in the outer box. The outer box includes an outer box body, a first lock portion to lock the inner box and a ground member to be electrically connected to a ground conductor, the ground member including a first ground contact portion provided at or adjacent to the first lock portion. The inner box includes an inner box body, a second lock portion to be engaged with the first lock portion, a ground circuit element to which the circuit base is connected to ground the circuit base and a contact conductor electrically connected to the ground circuit element, the contact conductor including a second ground contact portion to be electrically connected to the first ground contact portion when the first lock portion and the second lock portion are engaged with each other.