An airbag for a vehicle is proposed. The airbag includes an inflator configured to generate gas, the airbag cushion connected to the inflator and configured to expand by the gas, and a variable vent provided in a first side of the airbag cushion and configured to control opening and closing state of a vent hole of the variable vent for gas escape from the airbag cushion in response to an operational condition of the airbag cushion.