Cryogenic tensile properties of carbon nanocoil (CNC)/poly-dicyclopentadiene (poly-DCPD) composites have been investigated experimentally. Flat tensile specimens of CNC/poly-DCPD composites with 1.0 and 1.5vol.% CNCs were fabricated by an ultrasonic method and tested at room temperature (RT) and liquid nitrogen temperature (77K). The effect of ultrasonication time on the cryogenic tensile properties of CNC/poly-DCPD composites was discussed. A scanning electron microscope (SEM) was also used to observe the fracture surface morphology of CNC/poly-DCPD composites. Results indicated 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.