This paper discusses an adaptive algorithm to control a magnetorheological fluid vibration isolator operating under varying frequency of the vibration source. The algorithm provides automatic tuning of the isolator properties by controlling the viscosity of magnetorheological fluid in the throttle channels. This ensures efficient damping and vibration protection at the main harmonic of a varying vibrational frequency. The frequency finding approach utilised in the proposed adaptive control is much simpler than applying Fourier analysis and does not require significant computational resources. The control algorithm has been implemented into a FPGA based controller and tested using a laboratory vibration shaker. The test results demonstrated that the MR vibration isolator operating under the proposed algorithm provides an efficient damping at various vibrational frequencies.