The intestine, as the main organ of ethanol absorption, is susceptible to serious injury from excess drinking....We found that ethanol increased intestinal permeability, increased the release of lipopolysaccharide (LPS) into the circulation and destroyed the intestinal epithelial barrier structure in mice. Nicotinamide Riboside (NR) supplementation attenuated intestinal barrier injury. Both in vivo and in vitro experiments showed that NR attenuated ethanol-induced decreased intestinal tight junction protein expressions and maintained NAD homeostasis. In addition, NR supplementation activated SirT1 activity and increased deacetylation of PGC-1α, and reversed ethanol-induced mitochondrial dysfunction and mitochondrial biogenesis. These effects were diminished with the knockdown of SirT1 in Caco-2 cells. Conclusion: Boosting NAD by NR alleviates ethanol-induced intestinal epithelial barrier damage via protecting mitochondrial function in a SirT1-dependent manner.