This paper presents a new simple method for reducing mutual coupling between dual-element microstrip antennas (MSAs) for bi-static radar using a wave absorber. The two elements are closely placed on a substrate by the distance of λ₀/4 through the wall-shaped absorber. The height and width of the absorber were optimized for minimum mutual coupling with the electromagnetic simulator. It was found that less than -60dB minimum mutual coupling can be achieved by the impedance matching of the absorber in a near field. The influence for the reflection characteristics from the absorber is small enough, and the reduction of the antenna gain is only 1.1dB. The rate of the lost power characteristics showed that the absorption improves the mutual couplings. Then the proposed structure for a practical configuration was investigated. The measurement results of the optimized structure tallied well with the simulation results.