An object of the present invention is to provide a method of fixing an antibacterial agent, by which method it is possible to impart articles of a wide range of materials with excellent antibacterial property and good persistence of antibacterial activity. Specifically, the method of fixing an antibacterial agent, comprises the steps of: subjecting a surface of an article to a surface treatment of providing the surface with oxygen-containing functional groups； and then subjecting the article to a treatment using an antibacterial agent composition including a silicon-containing compound (a) represented by general formula (1) below. wherein R 1 represents a hydrocarbon group having 6 or more carbon atoms, R 2 and R 3 represent lower hydrocarbon groups, respectively, which hydrocarbon groups may be the same or different from each other, R 4 represents a divalent lower hydrocarbon group, R 5 , R 6 and R 7 represent lower alkyl groups or lower alkoxy groups, respectively, which may be the same or different from each other, and X represents a halogen ion or an organic carbonyloxy ion, or alternatively, first treating the article by using the antibacterial agent composition； and then subjecting the article to a 1-10 GHz microwave irradiation treatment in a state where the antibacterial agent composition remains on the surface of the article.
