The present invention relates to a disinfectant composition comprising hydrogen peroxide in association with at least one quaternary ammonium salt, suitable for disinfecting a room and the objects that may be therein contained. The composition is further characterized by the absence of ions of heavy metals and is particularly suitable for use in a method for the disinfection of a room, which comprises the diffusion of the present disinfectant composition in the form of a dry mist, maintaining contact with the room and with the objects therein contained, so as to obtain the desired degree of disinfection.