This study introduces the characteristics and application of nanotube-based smart composite materials to develop new sensors which are key devices of the fourth industrial revolution. Carbon nanotubes (CNTs), which are typical nanotubes, have been studied as sensor materials with piezoresistivity because they consist of continuous carbon atoms and have excellent electrochemical properties. Another nanotube boron nanotube (BNNT) structurally similar to CNT has piezoelectric properties as well as excellent material properties. Smart composite materials using nanotubes can be fabricated in nanocomposite processes and can be made flexible in macro or microscale using soft matrices. Therefore, it is expected that various sensors such as wearable motion sensor or artificial neuron for haptic can be liberally designed and economically manufactured, and that helps abundant interfaces between physical world and cyber space.