The present invention provides a liquid composition to make the mucous membrane bulge during endoscopic surgery characterized in that it comprises a chitosan derivative containing carbohydrate chains. The use of the composition of the present invention as a liquid for bulging the mucous membrane during endoscopic surgery, maintain the bulge of the mucous membrane for a long period, and prevent perforation, resulting in the improved reliability of endoscopic surgery. The composition of the present invention also demonstrates prevention and inhibition of bleeding from the incised portion. The introduction of a photo-reactive group to the above chitosan derivative with carbohydrate chains allows the easy formation of a hydrogel through photo-crosslinking, leading to the further improvement in retention of the bulge and prevention of bleeding.