An agent for treating acute respiratory distress syndrome includes, as an active ingredient, a lecithinized superoxide dismutase represented by the general formula (I):SOD′(Q-B)m (I)(wherein, SOD′ represents a residue of a superoxide dismutase； Q represents a chemical crosslinking； B represents a residue of lysolecithin, in which a hydrogen atom of a hydroxyl group is removed from the lysolecithin having the hydroxyl group at the 2-position of glycerol； and m is the average number of bonds of the lysolecithin relative to one molecule of the superoxide dismutase and represents an integer of 1 or more).
