Abstract: Mu opioid receptor in the digestive system and several organs of exterior structure of the Octopus ocellatus was observed and analyzed with immunohistochemical SABC technique. The results were as follows. Mu opioid receptor was not observed in the wrist, funnel, abdomen of mantle, mouth, craw, stomach theca, intestine, rectum, sialoid gland, liver. Weak positive mu opioid receptor immunoreaction was found in inner epidermis, ectoblast, connective tissue of the esophagus and the keratolytic of the stomach and positive immunoreaction in epidermis of back of mantle and membrane of wrist. The different density of mu opioid receptor may be referable to different function of organ.