A method and a device for removing sulphur dioxide from a gas, preferably a flue gas, by means of an aqueous suspension of an absorbent, preferably limestone, are disclosed. In the method, the flue gas is conducted through a conduit topped with an apertured plate (3) on which is provided a flowing layer of the absorbent suspension having a static height of at least about 100 mm, preferably about 200-500 mm, and a volume of about 50-500 l, calculated per m.sup.3 of flue gas flowing through the layer every second. The layer of absorbent suspension flows along the apertured plate (3) at a flow rate of about 5-100 l/s, preferably about 10-30 l/s per 1 m.sup.3 of sulphur-dioxide-containing gas per second. The device comprises an inlet (1) and an outlet (2) for the flue gas; an apertured plate (3); a tank (5) for the absorbent suspension; at least one inlet duct (6) arranged between the tank (5) and the apertured plate (3); means (8, 10, 11, 12) for supplying the absorbent suspension; at least one outlet duct (7) for recycling the absorbent suspension from the apertured plate (3) to the tank (5); and means (9, 12; 13; 14; 16) for supplying air, absorbent and water, as well as for withdrawing gypsum.