Hemolymph is an important defense line in insects. Hemolymph plays crucial defensive and immunological roles in insects. It includes hemocytes, the main immune cells, which perform various immunological functions such as phagocytosis, encapsulation, lysis of foreign bodies and release of humoral proteins. Two main immune responses that have been reported for insects are cellular and humoral defenses. Cellular immune responses are immediately carried out after an invasion of the hemocoel and include phagocytosis, nodulation and encapsulation. Insect hemolymph-derived peptides have a variety of therapeutic activities such as antimicrobial, anticancer and antiviral. The potential of these peptides to be promising effective agents for a panel of disease treatment makes them a main area of future research. The current review article explores some of the immune responses of insect hemolymph and the promising activities of their bioactive peptides.