The tensile fatigue behavior of a [0/ ± 45]s carbon/epoxy laminate with and without tightly consolidated epoxy-impregnated carbon nanotube (CNT) interlayers is evaluated. The interlayers contain either imperfectly aligned CNT yarns or aligned CNT films. Optical edge micrographs and measurements of loss factor, quasi-static elastic modulus, and tensile strength are compared before and after 106 cycles of fatigue loading at 3,000 or 4,000 με. X-ray radiographs were also recorded after 106 cycles. Though specimens with CNT interlayers had virgin tensile strengths similar to specimens without CNTs (baseline), the CNT interlayer specimens had less resistance to fatigue damage than the baseline. All the experimental methods employed could detect damage, though the direct imaging methods (edge microscopy and X-ray radiography) missed some early damage mechanisms, while quasi-static elastic modulus and especially loss factor measured below roughly 50% of the fatigue cycling strain were the most sensitive to damage. Edge microscopy uniquely showed that the CNT interlayers contributed to damage initiation and growth, presumably due to weak CNT/epoxy bonding or inadequate epoxy infiltration into the densely packed CNTs. After 106 loading cycles, the quasi-static modulus decreased by 3–5% and 5–12% for the low and high cyclic strain levels, respectively. Meanwhile, the 106-cycle residual tensile strength decreased by as much as 9–19% and 8–16% for the low and high cyclic strain levels, respectively. The baseline specimens showed no signs of damage in the micrographs and radiographs and negligible change in modulus and tensile strength over 106 cycles at either strain level.