Polyphenols are well known for its benefits to improve the antioxidant capacity and inflammation response in human but their positive response and underlying mechanism is not yet well established in fish. Therefore, a 60-day feeding trial was conducted to explore the effects of apple polyphenols (AP) for improving the health of grass carp. Fish were fed with plant protein based diets supplemented with 0, 1, 5, and 10 g of AP per kg. Results of the study showed that highest (10 g/kg) supplementation of AP exhibited lower growth of fish compared to other groups. Dietary inclusion of AP exhibited hepatoprotective effects via decreasing the activities of serum alanine aminotransferase, aspartate aminotransferase and γ-glutamyl transaminase (P < 0.05), and hypocholesterolemic effects. AP supplementation improved the antioxidant status in terms of high level of antioxidant parameters in serum and intestine tissue, followed by a reduction in malondialdehyde content (P < 0.05). Antioxidant capacity was improved by AP via activation of Nrf2, and over expression of catalase and copper/zinc superoxide dismutase (P < 0.05). Additionally, AP supplementation exerted an anti-inflammation effect through the inhibition of TLR4 signaling pathway, followed by a notable decrease in the transcription of pro-inflammatory cytokines like IL-1β, IL-6, and TNF-α (P < 0.05). Thereafter, an enhancement of intestinal barrier function was observed in AP1, AP5 and AP10 groups in terms of overexpression of junction proteins such as ZO1, ZO2, ZO3, and Occludin (P < 0.05). These results documented that AP exhibited beneficial impacts on the health of grass carp through improving antioxidant capacity, suppression of inflammatory responses, and enhancement of intestinal barrier function. Overall, optimal dose of AP for grass carp is 5 g/kg diet. • β-Glucan, inulin and emodin displayed hepatoprotective effects on grass carp. • Three additives significantly improved antioxidant capacity via Nrf2 activation. • Three additives attenuated the intestinal inflammatory responses. [ABSTRACT FROM AUTHOR]