A common pathogen of shrimp, Vibrio harveyi, was used in the present study. Firstly, the protease of V. harveyi extracellular products was isolated and purified to then be used in the subsequent evaluation of their effects on clotting factors and hemocyanin in white shrimp, Litopenaeus vannamei. The isolated and purified protease, being unstable in hyperthermal condition, possessed a molecular weight of about 22 kDa, an isoelectric point of 4.15, and its maximum activity was at pH 6 and 60°C. It is able to be inhibited by AEBSF, bestatin, EDTA, EDTA-2Na, 1,10-phenanthroline, iodoacetic acid, pepstatin A, phosphoramidon, PMSF, and L-cysteine, revealing characteristics of serine and metal forms. The 48 hours LD50 of V. harveyi extracellular products and purified protease injected into L. vannamei (5 ± 0.5 g) are 1.52 and 0.52 μg protein/g shrimp. The decreased coagulogen levels in haemolymph were observed in shrimps injected with of V. harveyi extracellular products and its purified protease; however, the effect on haemocyanin was insignificant.