Background: Hyperphosphatemia is a major adverse effect of chronic renal failure. It leads directly & indirectly through hypocalcaemia to hyperparathyroidism, which is the main determining factor of renal osteodystrophy. Hyperphosphatemia is now recognized as a major factor of hemodialysis morbidity and mortality. The control of hyperphosphatemia therefore represents a corner stone in the management of dialyzed patients (Llach &Bover, 1996 &London et al 2000). Current control is focused on reducing dietary phosphate intake &decreasing absorption using phosphate binders (Gutzwiller et al, 2002). Methodology: We have studied intradialytic and postdialytic phosphate and urea kinetics in regular (4 hours) and long (6hours) hemodialysis sessions in 30 chronic renal failure patients, 16 males & 14 females of age range 30-60 years old. Laboratory investigations (serum urea and phosphate) were done via taking blood samples from the arterial needle before the start of hemodialysis, then at five equally spaced time intervals during hemodialysis and at the end of the treatment without slowing of the arterial pump. Further samples were taken at 15 & 60 minutes post dialysis from the fistula needle for serum urea and phosphate. The patients were studied during a conventional hemodialysis session (four hours) and a long hemodialysis session (six hours) on the same day of consecutive week. Results: As regards phosphate clearance, there’s no significant difference between start and end of hemodialysis (P>0.05). While in urea clearance there’s significant change in serum urea concentration between start &60 min post dialysis in regular hemodialysis. In long hemodialysis session there’s significant difference between start of session &15min post dialysis &between end of session &15 min post dialysis (P<0.05).Conclusion: No significant difference between long and regular hemodialysis sessions as regards phosphate clearance, because there’s a third pool of unknown source yet. On the other hand urea clearance in long hemodialysis session is better than in regular dialysis dose.