Oyster plasma contains various soluble factors secreted by hemocytes and other cells, which were separated from the haemolymph and collected for antibacterial activity as-says. Plasma was collected after V. parahaemolyticus injection, with PBS injection being set as a control. Plasma of the V. parahaemolyticus challenged group was markedly more bac-tericidal than that of the PBS treated control。Peptidomics was herein employed to identify new bioactive peptides with antibacterial activity from plasma based on liquid chromatography and tandem mass spectrometry. To apply large-scale peptidomics to oyster plasma proteins, oyster plasma was extracted from the V. parahaemolyticus challenged group (P4, P5, P6) and PBS treated control (P1, P2, P3).