Endoscopic mucosal resection is performed by the steps of injecting a local injection preparation containing a biocompatible mucoploysaccharide having no anticoagulant activity, preferably sodium hyaluronate, into the submucosal layer of an affected mucosal tissue to create mucosal elevation, and then, trapping the thus-elevated mucosal tissue with a snare to perform resection. Preferably the local injection preparation further contains a hemostat or angiotonic, and a pharmaceutically acceptable dyestuff.