The monoclonal antibody (MAb) LITO-1 was produced from a stable hybridoma cell line generated by the fusion of NS1 myeloma cells with spleen cells isolated from Balb/c mice immunized with a paraformaldehyde-fixed hemocyte suspension of Litopenaeus vannamei. This MAb reacted with all three hemocyte subtypes, but no reaction was observed with components of plasma. Immunohistochemistry assays demonstrated that LITO-1 was very effective in specifically distinguishing hemocytes infiltrated in several tissues such as striated muscle, brain, and hepatopancreas. Moreover, this antibody was able to recognize hemocytes from two shrimp species, Litopenaeus schmitti and Farfantepenaeus paulensis, as well as hemocytes of the oyster Crassostrea gigas. No reaction was observed against hemocytes from the terrestrial insect Triatoma klugi or with mammalian RAW cells. This novel MAb can be useful in revealing the presence and function of a conservative epitope in hemocytes of marine crustaceans and mollusks.