Developing advanced technologies to address the bacterial associated infections is an urgent requirement for metallic implants and devices.Here,we report a novel phosphonate/quaternary amine block polymer as the high-efficiency antibacterial coating for metallic substrates.Three pDEMMP-b-pTMAEMA block polymers that bearing identical phosphonate segments (repeat units of 15) but varied cationic segments (repeat units of 8,45,and 70) were precisely prepared.Stable cationic polymer coatings were constructed on TC4 substrates based on the strong covalent binding between phosphonate group and metallic substrate.Robust relationship between the segment chain length of the polymer coating and the antibacterial property endowed to the substrates have been established based on quantitative and qualitative evaluations.Results showed that the antibacterial rate of the modified TC4 surface were 95.8 ％ ofS.aureus and 92.9 ％ of E.coli cells attached.Interestingly,unlike the cationic free polymer or cationic hydrogels,the surface anchored cationic polymers do compromise the viability of the attached C2C12 cells but without significant cytotoxicity.In addition,the phosphonate/quaternary amine block polymers can be easily constructed on titanium,stainless steel,and Ni/Cr alloy with significantly improved antibacterial property,indicating the generality of the block polymer for surface antibacterial modification of bio-metals.