Analysis of vehicle's vibrations, modelled by a two-degree-of-freedom system, is presented in this paper. The suggested quarter-car model is investigated in two variants: (I) with a conventional suspension composed of a linear spring and a bilinear damper, (II) a system with semi-active suspension, realized by magnetorheological damper (MR). For description of MR damping force, as functions of velocity and input current Bouc-Wen model is used. An open loop control, based on abstract sky-hook and ground-hook models and MR damping, is used for a vehicle oscillations reduction. Obtained vehicle body acceleration, a suspension deflection and a tyre displacement are compared for two considered variants of suspension. Advantages of semi-active vehicle suspension are emphasised.