Information concerning the concentrations of particulate substances in blood (e.g. erythrocytes, leucocytes, thrombocytes, apoptotic bodies, microvesicles, and exosomes) is important in disease risk prediction and judgment of health condition. However, as a problem of the conventional methods for obtaining concentration information, it is necessary to fractionate samples by size due to the limited measurement range of this technique. The Shimadzu Aggregates Sizer is an analytical device which measures the size and concentration of particles in liquids by the quantitative laser diffraction (qLD) method. Pretreatment by antibody reaction is not necessary, and it is possible to acquire data with high reproducibility in one measurement requiring only a few seconds. In addition, because the measurable particle size range is wide, if the sizes of the particles are different, the concentrations of each type of particle can be obtained without separation. This article introduces an example of measurement of blood with the Aggregates Sizer and quantitative evaluation of particulate substances in blood.