A method for treating tumor or inflammation in a patient in need thereof by administering a pH sensitive drug which includes a pH sensitive carrier including at least one amphipathic substance, and a physiologically active substance supported in the pH sensitive carrier to induce the pH sensitive carrier to develop a membrane disruptive function and to deliver the physiologically active substance to the site. The pH sensitive carrier can include at least one of deoxycholic acid, cholic acid, ursodeoxycholic acid, chenodeoxycholic acid, hyodeoxycholic acid, C27 bile acid, glycodeoxycholic acid, glycyrrhizic acid, glycyrrhetinic acid and salts thereof, and the amphipathic substance can include at least one of a phosphatidylcholine having 10 to 12 carbon atoms, a polyoxyethylene sorbitan monofatty acid ester having 12 to 18 carbon atoms, a sorbitan fatty acid ester having 16 to 18 carbon atoms, glycerol monooleate, glycerol dilaurate, glycerol distearate, glycerol dioleate, polyoxyethylene castor oil and α-tocopherol.