Abstract: The morphology and fine structure of the compound eye in Scylla serrata was observed with electron microscopes (EM).Under the scanning EM,there was a thumb-shaped area with no ommatidia on the back of the compound eye.Under the transmission EM,ommatidia were hexagon,which are specific to Decapoda Brachyura;the sensitization system of an ommatidium included 11 retinular cells (RCs),of which four located at the distal part of the ommatidium;seven formed the proximal main part of the retina.Thus a "4+7"structure could be seen at the conjunction area,partly in overlap.These observations are in keeping with those reported for Portunus tritubereulatus and the larval of Macrobrachium rosenbergii,but different from those with the structure of "1+7" in Libinia and Eriocher sinensis.The difference may be related to the dependence of the species on the visual sense in their natural habitats.