Late juvenile erythrocytes belong to a stage of erythrocyte development and are nucleated erythrocytes. Erythrocytes are categorized into primitive, early, middle, late, reticulocytes and mature erythrocytes according to their stage of development. Late juvenile erythrocytes begin to erythrocyte no longer divides, after denucleation to become reticulocytes, and then develop into mature erythrocytes, it takes about 48 hours. Primary red blood cells, early juvenile red blood cells, middle juvenile red blood cells, and late juvenile red blood cells are all nucleated red blood cells, which are normally found only in the bone marrow, and the main component of the blood is mature red blood cells, with a small amount of reticulocytes that may be present. Except for newborns within one week of age, the presence of nucleated erythrocytes in the peripheral blood suggests the possibility of hemolytic anemia, hematopoietic malignancies, and other diseases. Therefore, it is advisable to consult a physician to determine the cause of the disease if the patient’s blood is found to have late-onset red blood cells.