Three types of granulocytes, neutrophil, basophil and small eosinophilic granulocyte were observed in peripheral blood of threadfin shad Konosirus punctatus. The neutrophil had four types of granules, two types of eosinophilic granules (αG), chromophobic granule (βG) and basophilic granule (γG) in the cytoplasm. The αG was classified into two types, rod-shaped αG and round αG. The former was stained with various condition of May-Grünwald(MG), Giemsa and MG-Giemsa (MGG). On the other hand, the latter was stained with Giemsa and MGG, but not with MG. Acid phosphatase (AcP) and β- glucronidase (β-Glu) were detected in the round αG. Some esterases were also positive, however, alkaline phosphatase and peroxidase activity was not observed in the neutrophil. Basophil had three types of granules, type A, B and C granule. All types of granules were round or oval. The AG (≦0.7 μm) was the largest granules (BG and CG, ≦0.3 μm) and stained purple with MGG under a few conditions. The BG was not detected on the MG staining preparation, but stained purple with Giemsa and MGG. The CG showed light blue after MG, Giemsa and MGG stain. In basophil, AcP, β-Glu and some esterases were positive. Small eosinophilic granulocyte was small sized cell with condensed nucleus. The cell was round to oval, and had high nuclear to cytoplasmic ratio. Three types of granules, one major (eosinophilic granule) and two minor (chromophobic granule, basophilic granule), were observed in the cell. The AcP was detected in the granulocyte. Phagocytosis against zymosan particles was observed in only neutrophil.