Abstract: Objective To examine the possibility of early epigenetic alteration in perfluorooctane sulphonate(PFOS)-exposed rat liver.Methods Pregnant Sprague-Dawley(SD)rats were exposed to PFOS at doses of 0.1,0.6, and 2.0 mg/kg/d and 0.05% Tween 80 as control by gavage from gestation day 2 to 21.The dams were allowed to give birth and liver samples from weaned(postnatal day 21)offspring rats were analyzed for individual genes such as NAD(P)H:quinone oxidoreductase(NQO1)and carnitine palmitoyltransferase 1A(CPT1A)promoter methylation level.Results In PFOS exposed weaned rats,compared to the control,methylation of critical CpG sites in NQO1 promoter was found up to 10% methylated in the livers of treated rats.Conclusion Early induced hypermethylation in critical cytosines within the NQO1 gene promoter region may be a significant biomarker of hepatic PFOS burden,though their direct role in PFOS induced-hepatotoxicity,including its potential carcinogenic action,needs further research.