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[Display omitted] • A novel binary organic phosphonic acid was firstly integrated into nanofiltration membrane. • The rejection of membrane incorporated with AA was improved, while the permeability exhibited no decline. • Mono-/divalent anion selective separation factor surpass 500 even in high saline solution up to 20 g/L. • The membrane exhibit excellent chlorine resistance and anti-fouling performance. Nanofiltration membrane (NF) have become increasingly crucial in ion separation. However, traditional polyamide (PA) NF suffers from poor selectivity for mono-/divalent anions due to weak charges and structure defects. Thus, a novel binary organic phosphonic acid, alendronic acid (AA), was firstly used as an aqueous co-monomer via interfacial polymerization (IP) to create negatively charged nanofiltration membranes with both higher charge density and pore size homogeneity for the separation of mono-/divalent anions. Both structure characterization and performance tests demonstrated the successful introduction of AA in the separation layer. Compared with pristine membrane, the NaCl/Na 2 SO 4 selectivity of membrane incorporated with AA was four times improved, while the permeability exhibited no decline. Simultaneously, the separation efficiency of Cl-/SO 4 2- was tested in NaCl/Na 2 SO 4 binary mixed solutions with varying total concentrations and different mass ratios, and the separation factor consistently exceeded 500 across a concentration range of 1 g/L to 20 g/L. Moreover, the AA-integrated membrane exhibited excellent chlorine resistance after 20000 ppm·h of chlorine treatment, which is promising for high efficiency separation of mono-/divalent anions in industrial applications. [ABSTRACT FROM AUTHOR]