A chemically modified protein with insulin secreting activity which comprises an islet-activating protein produced by bacteria belonging to the genus Bordetella and polyethylene glycol moiety of the formula --O--CH2 CH2 O)l R where R is a protective group for hydroxyl and l is an integer of about 7 to 700, the polyethylene glycol moiety being bound with a primary amino group of the islet-activatin