Vibration control of a structure is an important issue in engineering that its application is more visible in aerospace, marine industry, manufacturing and production, etc. Vibration control is based on reducing or changing the vibration of a system, which reduces noise and mechanical stress in the system and instead increases the efficiency and reliability of the system. In this research, the vibration of the rotating saw blade in cutting process is investigated and an attempt is made to control these vibrations in a semi-active way by a magnetorheological damper. First, the rotating disk is modeled. Then, according to the natural frequencies of the system and the mode shapes of its modes, the location of the magnetorheological damper is determined. Magnetorheological damper is modeled, then by designing a controller suitable for this system, the damping coefficient of the damper, which depends on the input voltage of the system, is controlled, in order to reduce system vibrations. Keywords: Vibration, Rotating disk, Saw blade, Magnetorheological damper, MR damper, Semi-Active Control ?