High flux dialysis the first choice of therapy for hemodialysis patients within the last decade due to its clinical outcome. In this study the effect of dialysis environment on the mechanical and structural stability of high flux dialyzers containing polysulfone membranes were investigated. Dialysis sessions were performed on a certain group of patients with dialysis ages less than two years and without any other accompanying disease. Mechanical data and XRD results revealed the differences in material characteristics between virgin and used membranes obtained from polysulfone membranes. With the help of tensile tests it was shown that the mechanical properties used membranes were reduced in terms of ultimate tensile strength. XRD experiments revealed that the degree of crystallinity of the polysulfone dialysis membranes were raised. It was concluded that high flux dialyzer membranes are becoming more brittle and having more crystallinity after dialysis session. By this way the membranes are more prone to mechanical defects during dialysis. The degree of crytallinity increases under cyclic loading which resembles the changing of the pump speed or transmembrane pressure during dialysis in case of clinical situations like hypotension during dialysis. This issue is very important for dialysis centers performing reuse procedures for dialysis centers, because any damage to dialysis membranes would cause very serious clinical complications.