Abstract: In order to investigate the effects of injecting phosphatidyl serine(PS)on hemocyanin synthesis and hemocyanin-derived phenol oxidase(Hd-PO)and probe into the pathway and activating mechanism of PS as a possible native elicitor for Hd-PO in white shrimp(Litopenaeus vannamei),we injected adult white shrimps different PS with 5,10,20 μg/mL,and assayed hemocyanin concentration in plasma,expression of hemocyanin subunits(p75 and p77)and mRNA in hepatopancreas,along with Hd-PO activity in plasma from white shrimp.They were investigated by spectrophotometry,native-PAGE,SDS-PAGE and RT-PCR in vivo with different sampling time at 0,6,12,24,36,48 and 60 h respectively,and we set the control group and parallel group.The results showed that hemocyanin concentration declined slightly during 6 h after injecting PS and afterwards changed as a peak by 36^th h after injection with a maximum at 24^th h(P<0.05);expression of hemocyanin subunits and mRNA all had peak changes during 36 h after injecting PS,and likewise,all reaching their ceiling values at 12^th h(P<0.05);Hd-PO activity had a peak change within 36 h after injecting PS,with its climax at 12^th h(P<0.05).The research revealed that PS could activate hemocyanin to show phenol oxidase activity with significant time-dose effects,and meanwhile brought down hemocyanin concentration in a short time at first and subsequently started the hemocyanin synthesis,indicating that PS is the elicitor of Hd-PO in white shrimp,which lays the theoretical foundation for the study on immunological function of hemocyanin in shrimp.