A modified magneto-rheological rubber (MRR) which resistance can be reduced to 1KΩ was fabricated by dispersed multi-walled carbon nanotubes (MWNTs) and carbonyl iron particles (CIPs) into polydimethylsiloxane (PDMS) matrix. Based on the excellent piezo-resistive properties of this modified MRR, a MR bearing with self-sensing characteristics was proposed and systematic researched. In order to study the self-sensing characteristics of the MR bearing based on modified MRR under load and magnetic fields, the structure and working conditions of the bearing were simulated and compared. The optimal structure size of the bearing was selected and used for the build-up of experiment test system. The results showed that, under the action of preload condition by bearing, due to piezo-resistance and magnetoresistance behavior of the modified MRR, the electrical resistance of it also can be changed over 28%. It suggests that, in the MR semi-active vibration isolation system, the modified MRBs are potentially capable of being used as an actuator and sensor in the same time.