Quercetin (0.05~0.20 mmol/L, final concentration) obviously inhibited the aggregation and production of PGE2 and TXB2 of human PMN which were induced by AA ( 0.66 mmol/L), LTB4 ( 0.002 mmol/L) and the fourth composition of cobra venom of Guangxi Province ( 4.8mg/L) in vitro. These effects were dose dependent, the IDg50 of PMN aggregation induced by AA, LTB4 and the fourth composition of cobra venom of Guangxi Province was 68?mol/L, 59?mol/L and 61?mol/L respectively. At the concentration of 0.50?mol/L, it can also inhibit lysozyme release of PMN induced by AA, LTB4 and the fourth composition of cobra venom of Guangxi Province.