Biofilm formed during HD on dialysis membrane is not entirely removed by reprocessing Chemicals. This probably causes diffusion diminution of substances of larger molecular weight during consecutive HD sessions. The aim of the study was comparison of cuprophane (CUP) and polysulfone (PS) dialysis membranes’ surface nanostructure along with their changes assessment depending on the number of reuses, and evaluation of PS and CUP peracetic acid (p.a.) reprocessing influence upon small and middle molecule toxins’ actual dialyser clearance (KD). The markers were: urea, creatinine, uric acid and folie acid, respectively. Assessment of biocompatibility of studied new and reused dialysis membranes was determined by monitoring IL-6 and TNFα concentrations in patients’ serum. The dialysis membranes’ surface roughness measurements (RMS) were accomplished with atomie force microscopy (AFM), while dialysers’ performance was evaluated using the markers’ KD for new CUP and after 1, 2, 3, 4, 5th reuse number and for new PS and after 1, 3, 5, 7, 10th reuse number. Conclusions: Internal and external surface roughness of studied membranes discloses asymmetrical nanostructure of PS and symmetrical one of CUP. Reuse of dialysis membranes with p.a. does not affect their surface nanostructure. The clearances of small molecules’ markers remain stable. The results of middle molecules’ markers’ KD discl ; ose that allowed reprocessing number of CUP dialyzers is 3, of PS - 7. Reuse of studied dialysis membranes with p. a. does not improve their biocompatibility. No correlation between the dialysis membranes’ surface roughness and their biocompatibility was found.