INTRODUCTION: This study aimed to explore the effect of Clostridia administration on ovalbumin (OVA)-induced allergy and the relevant underlying mechanism in BALB/c mice. METHODS: Female BALB/c mice were assigned to three groups: control (C), OVA sensitization (CO), and intervention (IG). All mice were treated with antibiotics to eliminate their intestinal flora. Then, the mice in the CO and IG groups were orally treated with phosphate-buffered saline (PBS) and Clostridia extract, respectively, followed by OVA sensitization, while the mice in the C group only received PBS during the experiment. Allergic reactions, intestinal barrier function, and composition of the gut flora were analyzed. RESULTS: The CO group demonstrated significant allergic reactions when compared to the C and IG groups. The serum levels of interleukin-5 (IL-5) were significantly lower in the IG group than in the CO group. The levels of interferon-γ, transforming growth factor-β1, and T-helper 1 subsets were significantly higher in the IG group than in the CO group. The serum D-lactate level was significantly reduced in the IG group, while IL-22 levels were reduced in the CO group relative to the C group. In addition, tight junction proteins and mucin in the ileal tissues were significantly elevated in the IG group than in the CO group. The relative abundance of Clostridia_UCG014 and Christensenellales was significantly enriched in the feces of mice in the IG group and negatively correlated with the serum sIgG1 level. CONCLUSION: Clostridia alleviated food allergy symptoms in mice by regulating their intestinal immune function, improving the intestinal microbial composition, and enhancing the intestinal barrier.