In this paper, we present a suction cup by applying magnetorheological elastomers (MREs) that can be used for the wall climbing robot and picking application. MRE is a smart material in which the ferromagnetic particles are dispersed in the elastomer. In conventional research, MREs are often used as a vibration absorber, since the physical or mechanical properties can be altered upon the application of a magnetic field. In this paper, we focus on the expansion of the use of MRE material. When the magnetic field is added, the MRE will be attracted to the magnetic generator due to the ferromagnetic particles inside. The basic mathematical model between magnetic force and elasticity is discussed by us, which supports the working principle of building MRE suction cup. The MRE suction cup contains a permanent magnetic field generator unit and a MRE membrane unit. A servo motor is used to control the ON/OFF of the magnetic generator, so that the MRE membrane can be activated and deactivated. In this prototype, we focus on picking objects with flat surfaces as the first attempt. The proposed suction cup can achieve appropriate suction force, low noise, energy-saving. In this paper, the operation method of MREs, the design of the suction cup, and the evaluation of the prototype are conducted.