Rotavirus (RV) is a pathogen that induces severe diarrhea in infants and young animals. Shiitake mushroom is a traditional food, which can improve physiological function, including gut health. Lentinan (LNT) is the main functional component of Shiitake mushroom. This study aimed to verify whether LNT administration could improve intestinal barrier function, thereby decreasing RV-induced diarrhea in a porcine model. According to initial weight and origin, a total of 28 weaned piglets were randomly fed 2 diets containing 0 or 84 mg kg-1 LNT for 19 d (n = 14). On day 15, RV was orally infused to half of the pigs in each group. RV-induced diarrhea (P < 0.05), the positive rate of RV non-structural protein 4 (NSP4), impaired intestinal morphology, antioxidant capacity and microbiota (P < 0.05), and increased apoptosis of jejunal epithelial cells (P < 0.05) were assessed in the piglets. Dietary LNT supplementation was found to improve intestinal morphology, permeability, antioxidant capacity and microbiota (P < 0.05). Supplementation also further alleviated the effects of RV infection on diarrhea, intestinal morphology, permeability, antioxidant capacity, microbiota and apoptosis of jejunal epithelial cells in piglets (P < 0.05). Thus, these results suggest that LNT administration relieved RV-induced diarrhea in piglets, which could be due to the increase in antioxidant capacity, reduction in apoptosis and improvement of the microbiota-increased gut barrier.