<p>Oxidative stress has been found to burden dialysis patients relying on artificial kidney membranes. If the artificial kidney membrane itself had a higher antioxidant capacity, scavenging the reactive oxygen species generated during dialysis may be possible. However, no means to compare the antioxidant capacity of the membranes is currently available. Therefore, we developed a continuous-flow spin-trapping electron spin resonance (CFST-ESR) method to evaluate the superoxide radical (O₂^·–) scavenging capacity of artificial kidney membranes. In the flow-system of the CFST-ESR, O₂^·– was constantly produced on the membrane surface through the riboflavin dependent photo-reduction of solvated oxygen, and the resulted O₂^·– was quantitatively detected as DMPO (5,5-dimethylpyrroline-<i>N</i>-oxide) spin-adduct radical (DMPO/O₂). Comparison of ESR signal intensity of DMPO/O₂ provide information regarding the O₂^·– eliminating capacity of polysulfone made kidney membranes (PFs). Based on the results of CFST-ESR measurements conducted for standard and vitamin E coated PFs, the latter vitamin E coated PFs membrane exhibit a higher O₂^·– scavenging capacity than that of the standard one. The newly developed CFST-ESR method can provide guidelines for the development of an artificial kidney membrane that can reduce oxidative stress caused by dialysis, considering the modification of PFs membranes by antioxidants other than vitamin E.</p>