Background: Dried Whitmania pigra is used for the treatment of cardiovascular and cerebrovascular diseases in traditional Chinese medicine and hot water and alcohol extracts also have anticogulant activity. However, a lower molecular weight and more stable anticogulant is needed. Objective: The objective of the following study is to purify and characterize of an anticoagulant oligopeptide from Hirudo (Whitmania pigra Whitman). Materials and Methods: Gel filtration on Sephadex G 50, ion exchange on diethylaminoethyl cellulose, and semi prepared high performance liquid chromatography were used to purify Hirudo. Automated coagulation analyzer was used for evaluating anticoagulant activity. Molecular weight was measured by Matrix assisted laser desorption ionization time of flight mass spectrometry. Amino acid sequence of the oligopeptide was measured by amino acid sequence analyzer. Results: A new anticoagulant, named whitide, isolated from Hirudo was purified, with a molecular weight 1997.1 Da. Amino acid sequence of the oligopeptide was identified as Gly-Pro-ALa-Gly-Hyp-Val-Gly-Ala-Hyp-Gly-Gly-Hyp-Gly-Val-Arg-Gly-Leu-Hyp-Gly-Asp-Arg-Gly. The results revealed that its amino acid sequence had strong homology to various types of collagen. Conclusion: Whitide might be an orally anticoagulant for its hot and trypsin stable.