Abstract: In the present study, light microscopy, scanning electron microscopy and particle size analyzer were utilized to investigate hemocyte classification and characterization between two horseshoe crabs Tachpleus tridentatus and Carcinoscorpius rotundicauda. Hemocyte classification was based on cell size, nuclear-cytoplasmic(N/C) ratio, the morphology, and the number and size of cytoplasmic granules in the hemocytes. Three major types of hemocytes were distinguished in the two horseshoe crabs:the granular cell(GC), the semi-granular cell(SGC) and the hyaline cell(HC). GC was the major cell type in both horseshoe crabs; HC was the minor cell type with highest N/C ratio. The hemocyte types between the two horseshoe crabs had no significant differencesin staining and morphology. However, significant differences of total hemocyte counts were observed between males and females within each horseshoe crab species.