Viscosity is an important parameter which affects hemodynamics during extracorporeal circulation and long-term cardiac support. In this study, we have aimed to develop a novel viscometer with which we can easily measure blood viscosity by applying the electromagnetically spinning (EMS) method. In the EMS method, we can rotate an aluminum ball 2 mm in diameter indirectly in a test tube with 0.3 ml sample of a liquid by utilizing the moment caused by the Lorentz force as well as separate the test tube from the viscometer body. First, we calibrated the EMS viscometer by means of liquid samples with known viscosities and computational fluid dynamics. Then, when we measured the viscosity of 9.4 mPa s silicone oil in order to evaluate the performance of the EMS viscometer, the mean viscosity was found to be 9.55 ± 0.10 mPa s at available shear rates from 10 to 240 s-1. Finally, we measured the viscosity of bovine blood. We prepared four blood samples whose hematocrit levels were adjusted to 23, 45, 50, and 70 % and a plasma sample without hemocyte components. As a result, the measurements of blood viscosities showed obedience to Casson's equation. We found that the viscosity was approximately constant in Newtonian silicone oil, whereas the viscosity decreased with increasing shear rate in non-Newtonian bovine blood. These results suggest that the EMS viscometer will be useful to measure blood viscosity at the clinical site. © 2013 The Japanese Society for Artificial Organs.