A non-hemorrhagic, chymotrypsin-like serine protease, UFEII, was purified from the marine echiuroid worm, Urechis unicinctus, after a combination of chromatography steps. UFEII was monomeric, with an apparent molecular weight of 26.7 kDa via SDS-PAGE. The isoelectric point of UFEII was 4.03, and the maximum activity of the enzyme was observed at 50 A degrees C and pH 8.0. According to fibrin plate assays, UFEII could not only directly degrade fibrin and fibrinogen but also activate plasminogen. Further, UFEII preferentially hydrolyzed the fibrinogen gamma-chain, followed by the B beta-chains and A alpha-chains. Moreover, ufeII, full length of the gene encoding UFEII, was obtained by RT-PCR, degenerated PCR, and nested PCR. The ufeII was determined to be a 906-bp cDNA containing an open reading frame of 795 bp encoding a putative protein of 264 amino acids with a predicted molecular weight of 27.03 kDa. Besides, UFEII exhibited no hemorrhagic effect. Overall, U. unicinctus may represent a potential source of new therapeutic agents in thrombolytic therapy.