To obtain the subject agent high in synergistic sterilizing.bacteriostatic potencies by far smaller amount than single drug use, excellent in long-activity and, especially effective even in a reducing material by combinedly using a hydrogen peroxide-supplying compound and a specific halogenation compound in a specific ratio.

This agent combinedly contains a hydrogen peroxide-supplying compound and one or more than two kinds of compounds selected from a halogenated nitroalcohol compound of formula I (R1 is H, a halogen, an alkyl, etc.; R2 is H or an alkyl; X is a halogen), a halogenated dithiolane compound of formula II (X is a halogen) and a halogenated nitriloamide compound of formula III in a weight ratio of (1/20)-(40/1). Hydrogen peroxide is preferable as the hydrogen peroxide supplying compound. Preferably, 2,2-dibromo-2-nitro-1- ethanol or 2-bromo-2-1,3-propanediol as the compound of the formula I, 4,5- dichloro-1,2-dithiolan-3-one as the compound of the formula II and 2,2-dibromo-3- nitrilopropionamide as the compound of the formula III are respectively used.