The relative permittivity and the dielectric loss in various hematocrit values under static bovine blood condition have been measured by dielectric relaxation method for the possibility of real-time thrombosis detection with exploiting the electrical blood properties. As a result, the relaxation frequency of the electrode and the frequency of the red blood cells were observed at 20kHz and 2MHz respectively. The characteristic frequency showing the permittivity of the red blood cell membrane is within a range from 60kHz to 1MHz. Additionally, the time variations of the resistivity and the relative permittivity were observed at the characteristic frequency of red blood cells. The bottom point was observed in the decreasing pattern of relative permittivity when thrombi were formed in the electrode holder. This specific bottom point indicates the starting time of micro-thrombus formation from the visual check of thrombosis in the presence of the red blood cells. The experiments indicate the possibility of the real time thrombosis detection for implantable ventricular assistance devices, heart-lung machines and artificial kidney.