An extract for preventing or treating thrombotic diseases, particularly, an extract of at least one of leeches and earthworms having a molecular weight of no more than 5,800 daltons is provided, wherein the extract includes 15% to 38% amino acid, 40% to 60% saccharide and 0.3% to 1% hypoxanthine. Processes for preparation, pharmaceutical compositions and uses thereof are also provided. Compared to conventional arts, the extract has safety greatly improved and drug actions maintained and even improved.
