This paper focuses on the fatigue crack growth behavior of unidirectional C/PA6 composites subjected to hydrolytic aging at temperatures ranging from 100 to 140 °C. The fatigue crack growth properties were determined using a multi-ΔG control test method. The latter is fully automatic and allows measurement of crack growth rates at various ΔG levels. It was shown that the fatigue crack growth properties were highly affected by aging. Whatever the aging temperature, the crack growth rate was increased by about a decade after aging, and the fatigue crack growth properties are highly dependent on the molar mass. Finally, it was shown that the traditional Paris law does not allow a full description of the behaviour so the Hartman-Schijve relationship was applied to characterize the fatigue response.