In this paper, we have studied on the microwave absorbers in X-band (8.2-12.4 GHz) made of E-glass/epoxy composite laminates containing three different types of carbon nano materials such as carbon black (CB), carbon nano fiber (CNF) and multi-wall carbon nano tube (MWNT). We calculated the complex permittivity solutions for single-layer microwave absorbers and checked the effect of the solutions on the thickness and the absorbing bandwidth of the absorbers. The complex permittivities of the E-glass/epoxy composite laminates were measured at the frequency band of 0.5-18.0 GHz. The experimental results show that the real and imaginary parts of the complex permittivities of the composites were proportional to the filler concentrations and, depending on the types of fillers and frequency band, the increasing rates of the real and imaginary parts with respect to the filler concentrations were all different. These different rates can have great effect on the thickness in designing the single-layer microwave absorbers. The effect of the different rates was examined by using Cole-Cole plots. The absorbing performances of these three types of composite absorbers were measured and the -10 dB bandwidths were all about 3 GHz.