Background <p>Maintaining the integrity of the structure and function of piglet intestines is crucial for their growth and health. This study aims to evaluate the effects of an antibiotic free diet supplemented with bile acid on gut health and growth performance of weaned piglets, and to explore their regulatory mechanisms.</p> Methods <p>Thirty-two weaned piglets were randomly divided into two groups and fed either a basal diet or a basal diet supplemented with 350&#xa0;mg/kg bile acid.</p> Results <p>Dietary supplementation with bile acid increased the average daily gain (ADG) and final weight of piglets, and reduced the diarrhea incidence (<i>P</i> &lt; 0.05), which was verified to be related to the improvement of lipid absorption, amino acid transport, and intestinal barrier function. Bile acid increased the concentration of lipase and decreased the concentration of total cholesterol, total glyceride, low-density lipoprotein, and urea nitrogen in serum (<i>P</i> &lt; 0.05). Meanwhile, bile acid improved the mRNA expression of amino acid transporters in the intestine. On the other hand, bile acid decreased the pH values of the stomach, jejunum, and colon, and improved intestinal morphology (<i>P</i> &lt; 0.05). The real-time quantitative PCR results showed that bile acid increased the mRNA expression of Occludin and ZO-1 in the duodenum and ileum (<i>P</i> &lt; 0.05). Moreover, dietary bile acid supplementation altered the composition of the ileal microbiota in piglets and increased the relative abundance of <i>Ligilactobacillus</i>. In vitro, bile acid improved the repair of IPEC-J2 cells after injury and was shown to be associated with the activation of farnesoid X receptors (FXR) and increased expression of tight junction proteins and aquaporins (AQPs) proteins.</p> Conclusion <p>This study found that dietary bile acid supplementation promotes the intestinal health and nutrient absorption partially through the FXR/AQPs pathway, ultimately improving growth performance of piglets.</p>