Abstract: Chinese sturgeon, Acipenser sinensis, is in extremely Critically Endangered status. The Beijing aquarium plays a major role in supporting and promoting the conservation. The facility rears wild sturgeon individually which allows to conduct the research at an individual level. The blood cell is an important indicator of fish health in clinical diagnosis. In this study, the peripheral blood cells of 40 sturgeons distributed in 7 age groups (from 4 to > 30 years old including wild samples, and the first and second generations of offspring) were studied by light microscopy and transmission electron microscopy. The morphological results revealed that there were 6 cell types in the peripheral blood: Erythrocytes were oval shape with about (13.00—18.54) μm in length and (7.94—13.25) μm in width, and a few mitochondrion were observed in cytoplasm. Lymphocytes were round shape, with pseudopod cytoplasm bulge and many microvillus on the membrane. The size lymphocytes were (12.95—24.39) μm×(6.30—18.19) μm among the large cells and (7.51—12.84) μm×(5.91—10.89) μm among the small cells. Neutrophils were (9.45—22.69) μm×(9.18—17.85) μm, with kinds of nuclei types and many organelles were observed in cytoplasm. In addition, there were many special granules in cytoplasm. Eosinophils had round shape with size about (14.20—17.09) μm×(13.42—16.39) μm and they were rich in granules and organelles. Monocytes had multiple nuclei types and the shape was either round, oval or irregular shape with size about (14.95—21.93) μm×(8.89—18.79) μm. A large number of vacuoles and very few organelles were observed in cytoplasm. Thrombocytes had different shapes with (9.71—15.62) μm×(4.54—11.61) μm in size. Many small vacuoles were observed in cytoplasm, they appeared either alone or in clusters with many cells dividing. The size of blood cells from large to small follows the order as follows: monocyte, neutrophil, eosinophil, large lymphocyte, erythrocyte, thrombocyte and small lymphocyte. There was no significant difference on morphology and classification of haemocytes between different age groups. The average concentration of erythrocytes (RBC), leukocyte (WBC) and thrombocyte were (5.56±1.19)×10 ⁸ /mL, (16.53±4.94)×10⁶ /mL and (15.53±15.82)×10⁶ /mL, respectively. The percentage of large lymphocyte, small lymphocyte, neutrophil, eosinophil, and monocyte were (5.26±3.95)%, (77.74±11.73)%, (9.40±7.98)%, (1.90±2.06)% and (5.50±4.00)%, respectively. The RBC of 18 age and 11 age groups showed significant differences with the rest of groups (P<0.05). The WBC of 18 age had significant differences with age 4 group, and they all showed significant differences with other groups (P<0.05). The neutrophil and lymphocyte of >30 year-old sturgeon had significant differences with 4 age group, and they all showed significant differences with other groups. It was concluded that the blood cell ofAcipenser sinensis was at a low level of evolution; their immune system was mainly composed of lymphocytes, granulocytes and monocytes. The results are important to the health assessment and conservation research of Acipenser sinensis.