A single-mode-multimode-single-mode (SMS) fiber structure based stress/strain sensor is applied to monitor internal stress variations in magnetorhelogical elastomers (MREs) matrix. The liquid silicone rubber mixture with embedded fibers, i.e. SMS fiber and Fiber-Bragg-Grating (FBG), are enclosed into an aluminum mould for curing within a permanent magnet field at room temperature for 5 days. Then the cured sample is utilized for internal stress/strain measurement by applying different magnetic field intensity, of the results show that SMS structure has higher stress/strain sensitivity than that of FBG when a variable magnetic flux density was applied the MRE. The present investigation shows capability of using SMS sensor for online feedback and operation of MREs materials and commercial potential in medical and healthcare applications.