In this paper, semi active control of non-ideal mechanical system with Magneto-Rheological (MR) damper is presented. The setup composed of a motor operating on a structure with mass M connected to a fixed frame by a non-linear spring and with a linear viscous damper. From the investigations carried out it is possible to observe the DC motor influence on the vibrating system along with non-periodic motions with chaotic characteristic. To control this system linear viscose damper is substituted by MR damper. A semi-active control method, sky-hook control is used in this study. Our results suggest that the addition of a MR damper turns the phase space smoother and it is so effective to suppress chaos.