Cryogenic tensile properties of carbon nanocoil (CNC)/poly-dicyclopentadiene (poly-DCPD) composites fabricated by ultrasonic technique have been investigated experimentally. Tensile tests were carried out with flat tensile specimens at room temperature (RT) and liquid nitrogen temperature (77K). The effects of temperature, CNC volume fraction and ultrasonication time on the tensile properties of CNC/polyDCPD composites were discussed. A scanning electron microscope (SEM) was also used to observe the fracture surface morphology of CNC/poly-DCPD composites. Results indicate that the tensile strength of CNC/poly-DCPD composites at RT and 77K is affected by ultrasonication time and there is a trade-off between improving dispersion and damaging the CNC.