Isolation of acidic and basic model drugs by using pH sensitive poly(acrylic acid) grafted poly(vinylidene fluoride) (PAA-PVDF) cation-exchange membrane from biological fluids was reported. Effects of drug charge and lipophilicity on adsorption were also investigated. In the present study, basic model drugs adsorbed to a considerably greater extent onto the membrane than acidic drugs. Albumin was not adsorbed onto the membrane. Results of our study exposed, that electrostatic interactions between positively charged basic drug and negatively charged PVDF-PAA membrane were the most important factor affecting drug adsorption onto the membrane. Adsorption of acidic and basic drugs onto the PVDF-PAA membrane was not related to drug lipophilicity. The results of present study demonstrated that basic drugs adsorbed extensively onto the membrane, but albumin did not, proposing that PAA-PVDF membrane may be suitable for isolating basic drugs from proteinaceous biological fluids (i.e. serum) for subsequent monitoring and evaluation.