By using Penaeus chorion as a specific substrate, the hatching enzyme (HE) from Penaeus chinensis was purified by gel-filtration and ion-exchange chromatography, and characterized in terms of its molecular weight and enzymatic properties in this study. It was found that the molecular weight of Penaeus HE is about 43.0 kDa in SDS-PAGE. The Penaeus HE had obvious choriolytic activity, which was optimal at pH 6.0 and temperature of 40 degrees C, respectively. The Km value of the HE for casein was 7.47 mg ml(-1). The HE activity was almost completely inhibited by SBTI, p-APMSF, bestatin, and NEM, greatly inhibited by ovomucoid, TLCK, IAM, chymostatin, and PMSF, and slightly inhibited by pepstatin A, TPCK, LBTI, and leupeptin. These results indicate that the HE is most probably a trypsin-type serine protease. Besides of these, the HE was extremely sensitive to EDTA, Zn2+, Ca2+, Mg2+, and Cu2+. Combined with the results that the EDTA-pretreated HE activity could be perfectly recovered by Zn2+, it is indicated that shrimp HE is most probably a kind of Zn-metalloprotease.