Objective To observe the protection of aprotinin, ulinastatin and aminomethylbenzoic acid, aminomethylbenzoie acid on blood fibrinolytie system during cardiopulmonary bypass(CPB). Methods Thirty-six patients with rheumatic heart disease who were treated by valve replacement were randomly divided into three groups: aprotinin group (group A, 12 cases): aprotinin 2000 kU was added into the priming solution; ulinastatin and aminomethylbenzoic acid group (group UP, 12 cases): ulinastatin 12 000 U/kg and aminomethylbenzoic acid 10 mg/kg was added into the priming solution; aminomethylbenzoie acid group (group P, 12 cases): aminomethylbenzoic acid 10 mg/kg was added into the priming solution. Results There was no significant difference in CPB time and blood transfusion among three groups; the postoperative 24 h chest tube drainage in group UP was (443.3 ± 150.8) ml, in group P was (430.0 ± 178.3) ml and in group A was (290.0 ± 98.0) ml, there were significant differences between group UP, group P and group A (P < 0.05). There was 1 case of severe allergic reaction in group A. Conclusion Aprotinin, ulinastatin and aminomethylbenzoic acid, aminomethylbenzoic acid are effective in stabilizing blood fibrinolytic system and preserving platelet function during CPB, leading to less postoperative blood loss.