Abstract: Recent studies have shown fish mucosal immune system plays an important role in disease defense. In the present study,we examined the morphology of groupers (Epinephelus coioides) mucosal-associated immune tissues including skin,eye’s corn,gill,foregut and hindgut. The microstructures of these tissues were observed on the tissue sections using H-E staining,and the ultrastructures of immune cells were described using transmission electron microscopic technology. The results show several kinds of immune cells existing in mucosal-associated tissues including goblet cells,lymphocytes,macrophages,monocytes,eosinophils and nertrophils. There are many Goblet cells in skin epidermis,gill epithelial layer and lamina epithelialis,where they secret mucus to construct the first body defense line to pathogens intrusion. Lymphocytes are abundant in lamina propria of hindgut and gill sinusoids,and also observed in foregut lamina propria,basal layer of skin epidermis and between epidermis and dermis of skin. Lymphocyte’s distribution in mucosal tissues indicates mucus antibody may be mainly secreted by local ASCs (Antibody secreting cells). Phage cells and granules distribute similarly as lymphocytes and function as non-specific immune cells and antigen presenting cells in local mucosal sites. Immune cells haven't been observed in grouper eye’s corn. Density of immune cells in the gill sinusoids is significant higher than in peripheral blood. A series of interesting figures showing skin epithelia enveloping a substance has been described and speculated to a process of epithelia engulfing an exogenic substance. Antigen uptake and presentation of mucusal-associated immune tissue has been discussed. Immune cells distributed in mucosal tissues supply cell foundation for mucosal immune system to finish immune response independent of the systematic immune system. The non-specific and specific immune response of mucosal immune system,and whether the mucosal immune system is independent from the systematic immune system have also been discussed in this paper.