A bactericidal preparation to be applied in ventilation and air-conditioning equipment is characterised in that it comprises a nanosilver component in colloidal form containing nanosilver particles in an amount of 5-4000 ppm complexed with polyvinyl alcohol (PVA) in an amount of 0.01-15%, in the presence of sodium or potassium nitrate at pH from 4.8 to 6.2 and a stabiliser dispersant in an amount of 0.01-12%, and, preferably, in the presence of a polymer in the form of ethyl polymethacrylate with molecular mass of 0.01-4000 kDa, said nanosilver component having been modified in the presence of nitric acid with polyethylene glycol with molecular mass of 400 at an amount of 0.1-45% and 30% hydrogen peroxide in an amount of 0.1-100 g/L.
