Abstract: Objective: To study the levels of plasma endothelin and its effect on fibrinolysis in acuteleukemia, and its roles in developing and bleeding of leukemia. Methods: Plasma endothelin(ET)was measured with radioimmunoassay. Plasminogen activity was measured with aceta lysis chromogenesis. Tissue-type plasminogen activator activity and plasminogen activator inhibitor activity were measured with chromogenic substrates. Ddimer was measured with ELISA. Results: The levels of ET were higher in acute leukemia than those in normal controls, especially in primary and non-remission acute leukemia markedly higher, in the groups of complete remission were lower, but higher than those in the controls. The levels of ET were higher in leukemia with bleeding than those in without bleeding .ET and tissue-type plasminogen activator activity had negative correlation. Conclusion: ET not only had important value in diagonosis and prognosis of leukemia, but also had relation with bleeding in acute leukemia.The correlation of ET and tissue-type plasminogen activator activity indicated ET might play a role in regulating fibrinolysis serving as an antifibrinolysis factor.