The effects of some pathogen-associated molecular patterns (PAMPs) (laminarin, LPS and poly I:C) on total hemocyte counts (THC), phenoloxidase (PO) activity, superoxide anion production and lectin, prophenoloxidase, lysozyme, cytosolic manganese superoxide dismutase (C-MnSOD) and catalase (CAT) gene expression were studied. The results showed that the production or activity of most tested immune factors and the expression of most tested genes were up-regulated after stimulation with PAMPs, among which the highest value of lectin with 4.4 times as much as that of the control group appeared at 6 h in hemocytes, of CAT with 47 times as much as that of the control group appeared at 12 h in hepatopancreas, and with 2.7 times higher than that of the control group at 24 h of C-MnSOD in hepatopancreas after laminarin injection. The peak value of proPO, lysozyme and C-MnSOD appeared at 6 h in hepatopancreas, 24 h in hepatopancreas and 24 h in hemocytes after LPS injection, respectively. The highest expression level of lysozyme appeared at 12 h in hemocytes after poly I:C injection. However, significant decreases of PO activity in hemocytes and lectin expression in hepatopancreas were found after poly I:C injection, and a dramatic down-regulation of proPO expression from 3 h to 48 h was found in hemocytes after injection with laminarin, LPS and poly I:C. The results suggest that the shrimp immune response could be activated or inhibited by different PAMPs, and that the hepatopancreas also plays a key role by synthesizing immune factors.