Magnetorheological (MR) fluids with excellent rheological characteristics are capable of exhibiting very quick responses to control vibrations in machines and structures under seismic excitations. The damping properties of MR fluids can be controlled by varying the externally applied magnetic field and current to the fluid. In the present work, MR fluids with nanoscale suspensions were used to eliminate the need of additives and to minimize the settling. The resultant suspensions exhibit good magnetic behavior under damper with off-state and on-state rheology using cyclic load test. The result also showed that the maximum damping force of 2 kN (off-state) and 3.52 kN (on-state) was observed for the MR fluid containing 20 % iron particles in silicone oil. Additionally, the behavior of the MR damper on a reinforced cement concrete (RCC) frame subjected to cyclic loading was studied. To determine the efficiency of the MR damper, an RCC frame was casted and tested with and without damper. The results show that the incorporation of the MR damper reduced the displacement by 49 % and an increase in load carrying capacity of 55 % was attained compared with the RCC frame without damper.