Citric acid (CA) has been shown to have beneficial effects on the intestinal barrier in mice, potentially serving as an alternative to antibiotics. The study found that CA can increase body weight and stimulate cell growth by increasing the number of G2 phase cells in IEC-6 cells. It also improved the structure of the small intestine by increasing the ratio of villi to crypts and enhancing the growth of beneficial intestinal microorganisms, such as Bifidobacterium and Lactobacillus. Additionally, CA promoted the expression of tight junction genes like occludin, ZO-1, and claudin-1, which are crucial for maintaining the integrity of the tight junction barrier. Furthermore, CA reduced the inflammatory response caused by H9N2 avian influenza virus infection and inhibited viral replication. These findings suggest that CA fortifies the intestinal tight junction barrier, inhibits influenza virus replication, and boosts intestinal immune function.Citric acid (CA) has been shown to have beneficial effects on the intestinal barrier in mice, potentially serving as an alternative to antibiotics. The study found that CA can increase body weight and stimulate cell growth by increasing the number of G2 phase cells in IEC-6 cells. It also improved the structure of the small intestine by increasing the ratio of villi to crypts and enhancing the growth of beneficial intestinal microorganisms, such as Bifidobacterium and Lactobacillus. Additionally, CA promoted the expression of tight junction genes like occludin, ZO-1, and claudin-1, which are crucial for maintaining the integrity of the tight junction barrier. Furthermore, CA reduced the inflammatory response caused by H9N2 avian influenza virus infection and inhibited viral replication. These findings suggest that CA fortifies the intestinal tight junction barrier, inhibits influenza virus replication, and boosts intestinal immune function.