Abstract: Met-Enkephalin in different tissues of Octopus ocellatus was observed and analyzed with immunohistochemical SABC technique. The results showed that met-Enkephalin existed in the respiratory system, circulatory system, excretory system, reproductive system, suggesting that distribution of met-Enkephalin was comprehensive in the O.ocellatus. It was found that most tissues presented weak met-Enkephalin immunoreaction positive in the O.ocellatus. Met-Enkephalin was likely to accommodate respiration, circulation, excretion, procreate, incretion of O.ocellatus. And the different density of met-Enkephalin might be referable to different function of organs.