Knowing that carbon fibre reinforced polymers are sensitive to moisture through their interphases, carbon fibres sized with Bisphenol A diglycidyl ether have been fluorinated under a N2/F2 atmosphere to confer them a hydrophobic behaviour. Because of differences in reactivity of gaseous F2 between fibres and sizing, only the latter has been fluorinated, resulting in an interesting covalent fluorine grafting onto the fibres, which has been evidenced by Infrared spectroscopy, 19F Nuclear Magnetic Resonance and Energy-Dispersive X-Ray Spectroscopy. The hydrophobic behaviour has been observed through contact angle measurements. The carbon fibre structure remains unchanged, as seen thanks to X-Ray Diffraction and Raman spectroscopy studies, and tensile tests on single carbon fibres, even if a roughening, evidenced by Scanning Electron Microscope images, occurs. When compared to the bare fibres, the functionalization via sizing fluorination is less energy consuming since the treatment occurs at room temperature.