A liquid crystal is usually applied to displays of televisions and computers. The objective of this paper is to clarify the electrorheological effect of a liquid crystal under an external electric field and to make a fundamental study on a rotary-type damper using a liquid crystal. A controllabie rotarytype damper using liquid crystal with nematic phase is proposed and applied to the vibration suppression of a rotary shaft and a pendulum. Two disks are mounted inside a housing which is attached to the rotary shaft. These disks are free to rotate inside and relative to the housing. Damping is introduced by filling the space between housing and disk with liquid crystal. Damping torque is produced by the controllable viscosity of the liquid crystal. The results show that the torsional vibration of the rotary shaft, and the free vibration and parametric resonance of the pendulum are suppressed effectively.