An electromagnetic interference shielding device includes a frame, two first shielding members, and two second shielding members. The first shielding members respectively extend forwards from top and bottom sides of the frame. Each first shielding member includes an elongated first plate, and a number of longitudinally spaced first engaging portions protruding from an outer side of the first plate. The second shielding members are slidably and respectively coupled to front sides of the first shielding members. Each second shielding member includes an elongated second plate, and a number of longitudinally spaced second engaging portions protruding from an outer side of the second plate. The second shielding members are slid relative to the corresponding first shielding members, to allow the second engaging portions of the second shielding members to respectively align with or stagger from the first engaging portions of the corresponding first shielding members.