Abstract: Objective To investigate nitric oxide(NO)secretion level of spleenlym phocytes in male C57BL/6 mice after high dose and short time PFOS exposure.Methods Twenty four adult C57BL/6 male mice we redivided in to four groups.The mice were given 0,5,20 and 40 mg/kg PFOS by oral gavage every day for 7 days and then single cell suspension of splenocyte was prepared.After 48 hoursπculture,the supernatant was collected and the NO level was detected with Griess.Results The body weight of the mice exposed to 20 and 40 mg/kg of PFOS showed significant deterio ration from the ir pre-exposed baseline.Spleen and thymus mass were significantly decreased compared to the control after exposure to 20 and 40 mg/kg of PFOS.Further more,liver mass was increased in the mice of exposure groups.The NO secretion of 40 mg/kg PFOS group in comparison with normal C57BL/6 mice was significantly decreased(P<0.05).Conclusion High dose and short time PFOS exposu e could decrease the level of NOsecretion in mice which indicates that PFOS could suppress the activation of spleen macrophage.