This study investigates the effect of nanocarboxylic acrylonitrile butadiene rubber on the tensile fatigue behaviour of carbon fibre-reinforced polymer composites with dicyandiamide-cured epoxy matrix. The stress-controlled tension–tension fatigue behaviour at a stress ratio of R = 0.1 and maximum stresses between 400 MPa and 650 MPa was investigated for the case of carbon fibre-reinforced polymers with pristine and nanorubber-modified epoxy matrices with loadings of 5 phr, 10 phr, 15 phr and 20 phr. The results from the experimental tests show that the high-cycle fatigue life of the laminates with 15 phr of nanorubber-modified resin matrix was increased by a factor of two compared to the pristine matrix samples. Scanning electron microscopy images of the fracture surfaces also show an enhanced plastic deformation existing at the fibre–matrix interface and a lower extent of fibre pull-out; both contributing towards the enhancement of the fatigue performance of the carbon fibre-reinforced polymer composites.