In this research, the microwave shielding characteristics of the carbon fiber reinforced composites were studied. Carbon fiber-epoxy prepregs of 135 plies were laminated, hot-pressed and prepared for measuring the shielding effectiveness. Two kinds of carbon fibers with the modulus of 24 and 36ton/mm² were used and the fiber orientation angles of the composite sample were 0, 30, 60 and 90 degree, respectively. The experiments were carried out by using the network analyzer(HP 8510) in the corresponding frequency ranges of 1GHz-25GHz. As a result, the transmission loss was decreased as increase in the fiber orientation angle for the direction of the microwave. Especially, the composite sample with the fiber orientation of 90 degree shielded the microwave up to 99.9%(0.1% is only transmission power). Also the inverse proportional relationship between volume resistivity and shielding effectiveness in the typical isotropic materials were not established in the fibrous composite materials of this research. That is, in spite of the same constituent materials(such as fiber content, fiber grade), the shielding effectiveness as to the fiber orientation was revealed as a great differentiation. So, on preparing the fiber reinforced composites, the controlling of the fiber orientation within the composites must be considered for the shielding effectiveness as well as the mechanical properties of the fibrous composites.