Early process of peritoneal inflammation on rat by ultraviolet irradiation was studied histologically and scanning electron microscopic· ally. After 1 minute irradiation of ultraviolet, minimal exudation on mesothelium was found. After 15 minutes irradiation, microvillies on mesothelium were covered with exudate. After 20 minutes, fibrin fibers appeared on intact mesothelium. Though the fibers wafted in exudate, the fibers could be cleared up by irrigation of saline. After 30 minutes, white and red cells appeared on the nest of fibrin fibers. After 45 minutes, edema came out at subserosal layer. After 1 hour, mesothelium was covered with fibrin fibers, white and red cells. But the coated fur could be washed off by jet irrigation of saline and intact mesothelium benearth the fur appeared. These results indicate that washing a peritoneal cavity by saline after abdominal operation is of practical value to prevent a intestinal adhesion due to post operative intestinal inflammation. Inflammatory changes of intestinal mesothlium was clearly demonstrated by scanning electron microscope and these observations revealed that scanning electron microscope was very useful for the study of inflammation which occured on the surfaces of organs.