Abstract： Objective To study the effects of low-molecular weight heparin (LMWH) and adrenocortical hormone (dexamethasone) on the hemolysis of red cells of patients with paroxysmal nocturnal hemoglobinuria (PNH) in vitro. Methods Using Ham's test and micro-complement lysis sensitive test (mCLST), the changes in hemolysis of red cells from 6 typical PNH cases were examined after adding LMWH and dexamethasone in different concentrations into the test solution in vitro. The effects of LMWH and dexamethasone on the coagulation of the tested blood samples were also studied using the activated partial thromboplastin time (APTT) test. Conclusions Both LMWH and dexamethasone could inhibit hemolysis in PNH, and they showed a synergistic effect. Their mechanisms of inhibiting hemolysis differed from each other. Furthermore, a tolerable dose of LMWH induced a limited prolongation of APTT. LMWH might be useful for controlling acute hemolysis in patients with PNH and reducing the dose of adrenocortical hormone.