In order to study the effect of croton oil on the mucous cell in the mice intestin the experimental animals were injected with 0.1gm body weight of croton oil through intraperitoneally. They were sacrificed by ether anesthesia and obtained from distal small intestine and duodenum and colon, and fixed in 10% meutral formal. After embedded in paraffin, sectioned in 5 micro thickness, and stained with P.A.S (Periodic Acid Schiffis) reaction. The average number of the mucous cell was counted in each specimen over 20 fields under 450 magnification. The following results were obtained; 1) An average number of mucous cell began rapidly increase from 15 min and reached high average number after injection of croton oil of mucous cell from 30-60 min after injection. 2) An average number of mucous cell rapidly increase after injection of croton oil and were not reduced normal level by time lapsed 48 hrs. 3) The mucous cell showed with tape of time after injection of croton oil. A type and B type decrease and showed recovery C type decrease and recovery. 4) According to the above findings, it is presumed that croton oil accelerate secretion of mucin of the mucouse cell and production of mucin in growing mucous cell.