Background: Modified ultrafiltration has been thought as superior to conventional ultrafiltration for attenuating the consequences of hemodilution and systemic inflammatory response after cardiac surgery with cardiopulmonary bypass in children. We conducted a prospective randomized study to test the hypothesis that if modified and conventional ultrafiltration have similar clinical effects or not when a standardized volume of fluid is removed.Patients and Methods: 100 patients underwent variable surgical procedures for correction of congenital heart defect using CPB. All are less than 10 kg. They were equally divided in two groups. Each group underwent certain ultrafiltration technique e.g. either MUF or CUF technique.Results: There were no statistical differences between the two groups in age, weight, clamp time, total volume filtered, initial ventilation period, total ICU stay and total hospital stay. MUF group showed marked increase in postoperative Hct (39.46 % ± 2.03)than CUF group(36.4% ± 2.26) with less need for both intraoperative and postoperative blood transfusion and less total tube drainage (MUF 97.20 ± 27.72 ml , CUF 107.2 ± 42.08 ml ).There were marked increase in systolic blood pressure post filtration in MUF group(93 ± 5 mmHg) than CUF group(90.14 ± 5.72 mmHg) with less need for inotropic support. No significant change in total mortality and morbidity between two groups.Conclusion: On standardizing volume of filtrate, although there might be no difference between CUF and MUF in total mortality and morbidity, but still applying MUF may show more positive effect on reduction of postoperative blood transfusion, tube drainage and better initial postoperative systolic function. Recommendation for future studies: 1- Larger study population should be tested in more than single Centre.2- More detailed study on SIR and Hemodilution.3- At least one filtration method should be used for low weights and high risk cases.