To develop methods for noninvasively and quantitatively measuring blood glucose levels (BGL)., the degree of red blood cell (RBC) aggregation at a low shear rate were robustly evaluated by introducing two new parameters determined from changes in the scattering power spectrum of the echoes from the intravascular lumen before and after cessation of blood flow. The clinical significance of these parameters was discussed by comparing them with BGL obtained just before the ultrasonic measurements in one healthy subject. A correlation was found between one of the proposed parameters and BGL. However, the p value was not very high. One of the reasons for the decline of the correlation will be that some factors other than blood glucose also affect RBC aggregation. The proposed method has the potential for clinical application after elucidation of the various factors affecting RBC aggregation.