The present invention provides an antibacterial agent with water solubility and biodegradable feature, which contains a polymer composed of a segment A and a segment B wherein, the segment A has the chemical formula I, and the segment B has the chemical formula II. The molar content ratio of the segment A to the segment B in the polymer is 1:0.007 to 1.2, wherein n is 0 or 1, m is an integer of 0 to 2, m+n &ne 0, X is one of H, Na, K, NH4, 1/2Ca or 1/2Mg, and Y is one of Cl, Br or I.一種具水溶性及生物可分解性之抗菌劑,其包含一由一鏈段A及一鏈段B所構成之聚合物,其中,該鏈段A具有下列之化學式I:該鏈段B具有下列之化學式II:該聚合物中之該鏈段A與該鏈段B之莫耳含量比為1:0.007~1.2,且n為0或1,m為0~2之整數,m+n≠0,X為H、Na、K、NH4、1/2Ca或1/2Mg,Y為Cl、Br或I。