Serine protease from the head of Pacific white shrimp was purified by the following techniques: ammonium sulfate fractionation, Q-Sepharose HP ion exchange chromatography, and Sephadex G-100 gel filtration. The molecular weight was estimated as 32.8 kDa using SDS-PAGE. The optimum pH and temperature of the enzyme for the hydrolysis of casein were determined to be 10.0 and $40^{circ}C$. It was stable at pH range from 8.0 to 11.0 and had good thermal stability. $Pb^{2+}$, $Ca^{2+}$, $Mg^{2+}$, $Cu^{2+}$, and $Mn^{2+}$ could active the enzyme certainly when $Zn^{2+}$and $Hg^{2+}$ strongly inhibited the activity. The enzyme was inhibited by the general serine protease inhibitor (PMSF) and the specific trypsin inhibitors (TLCK, SBTI). The modification of various amino acid modifiers for the purified enzyme determined that the enzyme active center included tryptophan, histidine, and serine, moreover, arginine had a certain relationship with the enzyme activity.