The invention concerns a method for sterilisation by plasma of at least a object which consists in: placing the object(s) to be treated (50) in a treating chamber (10) substantially subjected to atmospheric pressure; introducing in said treating chamber one or several non-biocidal gas mixtures whereof at least one contains moisture; generating a plasma producing species from one of the gas mixtures by generating at least with a high voltage power supply (38) an electric discharge between a high voltage electrode (36) and a ground electrode (40), said electrodes being placed in said treating chamber; driving the plasma species outside the inter-electrode zone (30), towards the surface of the object(s) to be treated (50); and discharging the gas residues derived from the treatment outside the treating chamber. Moisture is directly introduced at the object to be treated or into the inter-electrode zone. The gas mixture contains at least 10 % of oxygen and 10 % of nitrogen and it preferably consists of ambient air. A relative moisture content ranging between 50 % and 100 % is present at the object to be treated. The invention also concerns various devices for implementing said method in particular for sterilising all types of medical objects.