Properties and defence applications of carbon nanotubes are discussed in the paper. Carbon nanotubes are important emerging materials, showing diverse unique and interesting properties, such as optical, electronic, magnetic and mechanical properties, at the same time high chemical reactivity as well, due to their quantum confinement effects, more important, these properties are tunable in some extend. Lots of applications such as strength-enhanced structure materials, radar-absorbing structure, armor, body armor, wearable thermoelectric devices, smart textiles, water purification, warfare agent sensors and flat panel display, and so on, can be found using carbon nanotubes.