A designing method of an electromagnetic wave absorber, whose obliquely incident electromagnetic wave attenuates more than 20 dB at 1.9 GHz, was investigated. In TE(transverse electric) wave, the matching boundary was moved toward the higher value of the real part and toward the lower value of the imaginary part of permeability, respectively, and the size of the matching boundary was decreased with increasing the incident angle. On the other hand, the matching boundary in the TM (transverse magnetic) wave exhibited the other way around to the case of TE wave. To design the electromagnetic wave absorber regarding the incident angle, it was found that the target frequency, thickness of material, and incident angle should be determined prior to the determination of the material constants of the composite within the matching boundary.