<p>An improved t-PA (tissue plasminogen activator) having a structure of natural t-PA deficient in a specific amino acid site of the first cringle domain and another improved t-PA obtained by partly mutating the deficient t-PA in serine protease site are created. The improved t-PA's have an antiinflammatory effect while maintaining preferable properties of natural t-PA, and have excellent stability against heat and acid and a long biologically half-life. The improved t-PA's can be effectively used for treatment of acquired diseases relating to intravascualr agglutination.</p>
