Abstract: Nano-selenium (nano-Se) exhibits growth-promoting and antioxidant properties, making it an ideal feed additive to replace traditional inorganic selenium. To explore the effects of dietary nano-Se supplementation on Paramisgurnus dabryanus, we formulated six experimental diets with nano-Se levels of 0, 0.1, 0.3, 0.5, 0.7, and 0.9 mg·kg⁻¹. We had fed the juveniles with an initial body mass of (1.61±0.45) g by these diets for 60 d so as to evaluate the effects on antioxidant capacity and tissue morphology. The results show that the 0.3 mg·kg⁻¹ group had significantly higher mass gain rate and specific growth rate compared with the other groups (p<0.05). The activities of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) followed a quadratic trend, peaking in the 0.3 mg·kg⁻¹ group, while the catalase (CAT) activity reached its maximum in the 0.5 mg·kg⁻¹ group. The malondialdehyde (MDA) content was significantly lower in the 0.3 mg·kg⁻¹ group (p<0.05). Histological analysis reveals that the intestinal villus height, width, and muscular layer thickness were significantly greater in the 0.3 mg·kg⁻¹ group compared with the control (p<0.05). The findings indicate that nano-Se promotes the growth performance, enhances the antioxidant capacity, and improves the intestinal morphology of P. dabryanus. Based on the binomial regression analysis of mass gain rate and specific growth rate, the optimal dietary nano-Se supplementation level is 0.36 mg·kg⁻¹.