A viscometer based on velocity attenuation of rotating cylinder is presented in the paper. A solid rotor motor drives the cylinder immersed in liquid in a cup to a scheduled velocity. The electricity supply of the motor is cut, the velocity of the cylinder with rotor of the motor attenuates with time because of viscous torque and other resistance torque. The velocity is measured by optical encoder. Viscosity of the fluid was calculated by a computer. Experiments are carried out and results show that deviation of viscosity beyond 1000 mPa•s are below 3%. The viscometer can be used in measurement of viscosity beyond 1000 mPa•s in industry.