Morphological characteristics of hemocytes in some crustaceans were examined by light microscopy. Only a single type of hemocyte（granulocyte）was observed in Daphnia obtusa（Cladocera, Phyllopoda, Branchiopoda), Argulus sp.（Arguloida, Branchiura, Maxillopoda）from threadfin shad Konosirus punctatus, four podocopids（Heterocypris incongruens, Heterocypris attenuate, Hemicypris mizunoi and Stenocypris major, Podocopa, Ostracoda, Maxillopoda), Vargula hilgendorfii（Myodocopa, Ostracoda), and Neomysis japonica（Mysida, Eumalacostraca, Malacostraca). On the other hand, plural hemocyte types were detected in some eumalacostracans, three cymothoids（Flabellifera, Isopoda, Eumalacostraca), Porcellio scaber（Oniscidea, Isopoda), five brachyurans（Thalamita sima, Sphaerozius nitidus, Eriocheir sinensis, Chiromantes dehaani and Pachygrapsus crassipes； Decapoda, Eumalacostraca）and two anomurans（Spiropagurus spiriger and Paralithodes camtschaticus； Pleocyemata). Based on these results and those of other crustaceans previously examined, we make a speculation about the evolutional process of crustacean hemocytes as follows（a possible story). １. Ancestor in Crustacean had only one type of hemocyte, because of single type of hemocyte was observed in the primitive crustaceans such as branchiopods, maxillipods and primitive malacostracan（phyllocarid). ２. Pluralism（=Increase）of hemocyte type occurred in the common ancestor species of both Hoplocarida and Eumalacostraca, and the ancestor had eight types of hemocytes, because of the hemocyte-type（type I）was observed in the stomatopods and some eumalacostracans. ３. Other hemocyte-types（type II, four hemocyte types； type III, three hemocyte types; type IV； two hemocyte types; type V, two hemocyte types； pseudomonohemocytic type）in eumalacostracans appeared as a result of simplification（=decrease）of hemocyte types.