Abstract: The radar wave absorbing properties of aligned carbon nanotubes (ACNTs) were investigated. Aligned carbon nanotubes were grown by chemical vapor deposition (CVD) process. Then the films of ACNTs were put on the surface of an aluminium plate and were fixed by epoxy resin to prepare the samples. Aligned carbon nanotubes were characterized through TEM and SEM. The photos of SEM and TEM show the carbon nanotues in the films were well arranged with same orientation and have a diameter of 30-50 nm . The radar wave absorbing properties were obtained through radar absorbing materials (RAM) measuring system of arch method reflectivity. The results indicated aligned carbon nanotubes have excellent radar waves absorbing properties in the higher band of 2-18 GHz. The radar waves absorbing properties changed with the film thickness. The best parameters of RAM are obtained at 0.2 mm film thickness of ACNTs. The highest absorbing peak reaches -15.87 dB at 17.83 GHz and has a bandwidth of 4.25 GHz(R<-10 dB)and 6.40 GHz (R<-5 dB)respectively.