Abstract Polyvinylchloride based heterogeneous cation exchange membrane was modified by using in situ polymerization of polyacrylic acid and multi walled carbon nano tubes simultaneously. Spectra analysis confirmed graft polymerization decisively. SEM images illustrated that grafted-PAA/MWCNTs filled the cracks in membrane by simple gel network entanglement. Ion exchange capacity was improved by PAA/MWCNTs grafting in modified membranes. Membrane water content was decreased by PAA grafting and then showed increasing trend by using MWCNTs in modifier solution up to 0.1%wt. Water content was decreased again by more MWCNTs loading ratio. Grafted-PAA membranes showed lower membrane potential, transport number, selectivity and flux compared to pristine membrane in sodium chloride ionic solution. These parameters were decreased more by using MWCNTs up to 0.1%wt in modifier solution and then showed increasing trend by more MWCNTs concentration from 0.1 to 0.3%wt. All mentioned parameters were declined again by more increase in MWCNTs content from 0.3 to 1.0%wt. Results exhibited lower membrane selectivity for the modified membranes compared to pristine ones in bivalent ionic solution. The grafted-PAA/MWCNTs modified membranes also showed lower electrical resistance compared to unmodified ones. Obtained results showed different behavior for permeability in bivalent ionic solution compared to monovalent type.