Abstract: To evaluate the protection effect of nanoselenium (NSe) on the antioxidant capacity and histopathology of Cyprinus carpio liver under fluoride stress, a total of 750 C. carpio individuals were randomly divided into five groups, i.e., no fluoride stress and NSe addition (CK), fluoride (100 mg F^-·L^-1)stressed (FS), and fluoridestressed plus NSe added with a dosage of 0.1 mg Se·L^-1 (NSe L), 0.5 mg Se·L^-1 (NSe M), and 1.0 mg Se·kg^-1 (NSe H). The NSe was mixed with fish foods, and the fishes of FS and NSe groups were exposed to the fluoride stress for 30 days. As compared with CK, fluoride stress decreased the SOD, CAT, and GSHPx activities and increased the MDA content of C. carpio liver, and induced a definite damage on the histopathology of the liver. Compared with FS, NSe increased the liver SOD, CAT, and GSH-Px activities, decreased the liver MDA content, and mitigated the damage of fluoride stress on the histopathology of the liver. The results demonstrated that in some extent, the addition of NSe into fish foods could alleviate the decline of the antioxidant capacity of C. carpio liver and the damage on the liver histopathology caused by fluoride stress.