The effect of treatment of regenerated cellulose fibres by cellulose nanocrystals on the moisture absorption of the fibres as well as on fibre–epoxy resin adhesion has been investigated. Nanocrystals were deposited on the fibres using γ-methacryloxypropyltrimethoxysilane (MPS) as coupling agent. Water absorption tests performed on fibres showed that, at 64% relative humidity, treatment by the coupling agent decreased the water uptake by a factor of two compared with untreated fibres, whereas deposition of cellulose nanocrystals (CNC) on fibres treated with MPS (FMMPS) did not further increase the water absorption despite the hydrophilic character of the CNC. This result was confirmed by monitoring fibre swelling using contact angle measurements. Indeed, it was found that FMMPS presented the same contact angle with glycerol before and after CNC deposition, being higher than that obtained for untreated fibres. The tensile strength and stiffness of fibres were not affected by moisture after either treatment, but nanocrystal deposition enhanced the fibre–epoxy resin adhesion, as revealed by results of pull-out tests performed on fibre bundles at 64% relative humidity.