An apoptosis-related serine protease (ARSP1) was purified from Eisenia fetida extract (mainly a group of anti-tumor protein components) by hydrophobic interaction chromatography and ion exchange chromatography. The molecular mass assayed by SDS-PAGE and isoelectric point of ARSP1 were 28 ku and less than 3.8, separately. However, several coterminous bands could be observed by PAGE of natural ARSP1 and several coterminous peaks of ARSP1 were also detected with MALDI-TOF-MS when the relative molecular mass of three main peaks are 24 645, 25 052 and 25 281, separately. The N-term amino acid sequence of ARSP1 was assayed as following: I(V)IGGT(S)N(D)ASPGEFPWQLSQTRGGSHS. And, a result that ARSP1 is highly homologous with serine proteases was concluded by the comparison of N-term amino acid sequences. In vitro, the cytotoxicity of ARSP1 was not only identified by phase-contrast microscopy observation of apoptotic cells, but also studied further by the localization of fluorescent antibodies. By Schiff's staining, ARSP1 was identified to be glycoprotein or glycopeptide. By fibrin plate assay, ARSP1 was identified to be a plasmin and also a plasminogen activator, and the fibrinolytic activity was inhibited by PMSF (an inhibitor of serine proteases).