The purpose of this study is to present the optimal design technology on the broad band radar absorbing composite laminates. The design concept is based on the 2-layer Dällenbach type radar absorber, in which the composite laminates act as the lossy layers. The radar absorbing function was achieved by controlling the electromagnetic property of the composite laminates by means of adding carbon nano materials into the matrix resin of the fiber-reinforced composite laminates. The laminates were fabricated with the E-glass fabric/epoxy prepregs and cured in an autoclave. The electromagnetic properties were measured for the frequency band of 0.5 ~ 18.0 GHz using a coaxial air line and a vector network analyzer. The radar absorbers were designed to have optimal absorbing performance in 10 GHz. The optimization was conducted to get the optimal number of the plies of the laminates and filler contents of the carbon nano materials in the respective layers. The performances of the fabricated absorbers were measured to be compared with the design results. The discrepancy between the design and the measurement was discussed.