A helicopter anti-torque system significantly contributes to radiated noise. The Fenestron™ anti-torque system used on Airbus helicopters, reduces this noise through masking effects and blade distribution modulation. This paper explores integrating acoustic treatments into the Fenestron™, similar to those used in aircraft engine nacelles, to further decrease the anti-torque system noise. Numerical simulations are performed to identify the optimal acoustic impedance for these liners, followed by proposing and assessing several liner designs on small-scale experimental benches. Finally, a larger-scale, more representative measurement campaign on a Fenestron™ mock-up with integrated liners demonstrates that a likely significant noise reduction can be attained.