A side curtain airbag for a vehicle includes a serial main chamber that inflates and deploys along an interior side surface of the vehicle; a protruding chamber disposed at a front side of the main chamber to further protrude toward an interior of the vehicle relative to the main chamber; and a cutting line arranged between the main chamber and the protruding chamber to partially separate the protruding chamber from the main chamber such that the protruding chamber overlaps with a portion of the main chamber upon non-inflation of the airbag. In this configuration, upon a vehicle collision, the head portion of the occupant is prevented early from being ejected toward the front of the vehicle.