Background: low dialysate temperature dialysis has been used successfully in treatment of intradyalytic hypotension and resistant pruritus. In both conditions complement activation was proposed as one pathological mechanisms for their development. to our knowledge, no study has been done to assess the effect of low dialysate temperature on the individual complement activation pathway. Objective: to assess the effect of low dialysate temperature on complement activation pathways. Patients and Methods: this case control study included 20 patients, on regular hemodialysis at Alhusein University Hospital. Results: the mean age of our patients was 48.8±10 years, 11 males and 9 females, their mean BMI was 22±4 kg/m2 , their mean blood pressure 120/80± 20/20, all patients received hemodialysis via arterio-venous fistula. The main cause of hemodialysis is chronic renal failure due to hypertension in 8 patients, glomerulonephritis in 4 patients, polycystic kidney in 2 patients, hyperurecemic nephropathy in 2 patients, analgesic abuser in 1 patient, and chronic pyelonephritis in 1 patient. Conclusion: cold hemodialysis is associated with activation of complement system.