Abstract: We applied Wright's staining as well as cytochemical techniques and phagocytosis test to investigate morphological characterization and immune function of blood cells in "Youlu No.1" largemouth bass (Micropterus salmoides). Two types of blood cells were recognized: erythrocytes and leukocytes, including monocytes, thrombocytes, lymphocytes and granulocytes (Type Ⅰ, Ⅱand Ⅲ). Erythrocytes were the predominant blood cells, while leukocytes were relatively less. Lymphocytes were the most numerous among the leukocytes, accounting for 62.73%. Erythrocytes were negative by cytochemical properties of periodic acid Schiff (PAS), Sudan black B (SBB), acid and alkaline phosphatase (ACP and AKP), peroxidase (POX) and phenoloxidase (PO). All the leukocytes were positive for PAS, SBB, ACP and PO except for AKP and POX. Moreover, there were some differences in the degree of dyeing among the leukocytes. Thrombocytes were stained intensely with PAS, SBB, ACP and PO. Phagocytosis test reveals that erythrocytes show active phagocytic function with phagocytic rate of (16.17±1.08)%. Furthermore, thrombocytes, granulocytes (Type Ⅰ, Ⅱand Ⅲ) showed immune adherence function. Thrombocytes adhered to yeast, forming complex rosette, showing active immune adherence function which might be related with high degree of shape alterations and abundant PAS, SBB, ACP and PO that would influence phagocytosis of thrombocytes.