A roof airbag for a vehicle includes: an airbag cushion located at a roof panel of the vehicle and configured to be unfolded from a first side portion to a second side portion of the roof panel during an operation of the airbag cushion; a first seam portion extended in a direction intersected with an unfolded direction of the airbag cushion and allowing upper and lower surfaces of the airbag cushion to be in contact with each other; and an inflator coupled to the first side portion of the roof panel, and connected to the airbag cushion and configured to inject gas into the airbag cushion so as to allow the airbag cushion to be unfolded from the first side portion to the second side portion of the roof panel.