Abstract: Provided is a chair for a ship with horizontality maintaining structure for preventing passengers on board the ship from getting motion sickness by maintaining the horizontality of the chair installed in cabins and the like in response to wobbles of the ship. The chair for a ship with horizontality maintaining structure according to the present disclosure includes an external frame 10 which is installed in a fixing way on the hull floor; an internal frame 20 which is integrated inside the external frame 10 so that it rotates back and forth; a seat unit 30 which is integrated inside the internal frame 20 so that it rotates from side to side; and a horizontality maintaining means 40 which is formed in the lower part of the seat unit 30.