An antithrombotic containing dermatan sulfate or a pharmacologically acceptable salt thereof (DS) as the active ingredient. The use of a DS derived from a crest or a disaccharide component thereof having a DELTA Di-OS value of at least 3 % or a molecular weight of at least 25 thousand serves to maintain an effective blood level for long and conduct efficiently thrombus dilation or prevention. When used together with a tissue plasminogen activator (t-PA), DS can accelerate remarkably thrombolysis and reduce the amount of t-PA used. This drug is useful for treating and preventing various types of thrombosis such as myocardial infarct and disseminated intravascular coagulation syndrome. Further it can inhibit blood coagulation in extracorporeal circulation such as renal dialysis.
