The experiments were performed to investigate the change of erythrocyte count, proportion of reticulocytes, hemoglobin, volume of packed red cells, mean corpuscular volume, diameter, hemoglobin and hemoglobin concentration, leucocyte count and differential count of leucocytes in the blood of the rabbit during pregnancy, parturition and lactation, and also the development of fetus and infant. The results are as follows. (1) The count of erythrocytes begin to increase rapidly from the late stage of pregnancy and the count reaches maximum level at the 25th day of pregnancy. But thereafter the count of them very decrease and reaches minimum level at parturiton. It recovers to a normal value on one month after parturition. The amount of hemoglobin does not show a marked change during pregnancy, parturition and lactation, but it decreases slightly from before to after parturition. The hematocrit, volume of packed red cells decrease rapidly from the late stage of pregnancy and the volume reaches minimum level at parturition, but thereafter it increases gradually and recovers to a normal value on one month after parturition.The mean corpuscular diameter and volume become small gradually from the late stage of pregnancy and it reaches minimum level at the 25th day of pregnancy, but thereafter it becomes large in size and recovers to a nomal value on one month after parturition. The mean corpuscular hemoglobin decrese gradully from the late stage of pregnancy and it reaches minimum level at the 25th day of pregnanancy, but thereafter it increases and recovers to a normal value on one month after parturition. The mean corpuscular hemoglobin concentration increase rapidly from the late stage of pregnancy and it reaches maximum level atparturion, but thereafter it decreases and recovers to a normal value on one month after parturition. The proportion of reticulocytes, the count of leucocytes and differential count of leucocytes remain a fairy constant during pregnancy, parturition and lactation. (2) It is found that the red cell count, hemoglobin, volume of packed red cells, the white red cell count and lymphocyte count are in very younger fetus very low as compared with those of the mother, whereas the proportion of reticulocytes, mean corpuscular volume, diameter, hemoglobin and hemoglobin concentration and neutrophile polynuclear leucocyte count are very high. As the fetus develops, the red cell count, hemoglobin, volume of packed red cells, the white red cell count and lymphocyte count increase, whereas the proportion of reticulocytes, mean corpuscular volume, diameter, hemoglobin and hemoglobin concentration and neutrophile polynuclear leucocyte count decrease. And also as the newborn grows, the number of red cells, white cells and lymphocyte count increase, whereas the amount of hemoglobin, proportion of reticulocytes, mean corpuscular volume, diameter, hemoglobin and hemoglobin concentration and neutrophile polynuclear leucocyte count decrease, but a few ones of them, that is, the amount of hemoglobin, volume of packed red cells and mean corpuscular hemoglobin begin to increase on 10-20 days and reaches the adult value on 2-3 months after birth.