Cellulose nanofibre coatings were treated by a dielectric barrier discharge plasma in a He/NH3 gas mixture at atmospheric pressure. Ultrasound was optionally irradiated during the treatment. The treatment enhanced the wetting of deionized water, glycerol, and uncured epoxy. Irradiation of ultrasound did not significantly change optical emission from the plasma, but increased the oxygen contents and enhanced etching and roughening at the nanofibre coating surfaces. Furthermore, the irradiation of ultrasound enhanced the wetting of deionized water and glycerol drastically, while that of uncured epoxy to some extent.