Disclosed herein are exendin singly modified with polyethylene glycole or a derivative thereof, a method for the preparation of the same, and uses thereof. Exendin modified at lysine (27) with polyethylene glycol shows biological activity similar to that of natural exendin, but is improved in half life. In addition, the modification position and the number of PEG or its derivative are restricted so as to minimize the side effects caused by a variety of combinations of such factors. The exendin is useful in the prevention and treatment of diseases caused by the over-secretion of insulin, or diseases caused due to a decrease in plasma glucose level, the inhibition of gastric or intestinal motility, the promotion of satiety, or the inhibition of food intake, especially diabetes, obesity and irritable colon syndrome.