Background: Probiotics are mainly distributed in the mucosal system and have the ability to enhance mucosal barrier function and regulate immune responses. Broncho-Vaxom (BV), as a probiotic, has been applied to patients suffering from respiratory tract infections, but its potential effectiveness in allergic rhinitis (AR) has not been evaluated in human. This study aimed to investigate the clinical efficacy of BV in patients with persistent AR and to elucidate the underlying cellular mechanisms.Methods: Sixty patients with AR were enrolled to this study and were randomly assigned to the BV group (n=30) and the placebo group (n=30). Changes of clinical symptoms and laboratory parameters of allergic inflammation were measured at baseline visit, immediately after BV treatment, four weeks, and eight weeks after the BV treatment.Results: After BV treatment, medication score in the BV group was significantly decreased compared with placebo group, along with a significant drop of the total nasal symptom score and the individual nasal symptom scores (itching score: 23.72±5.32%; nasal rhinorrhea score: 18.59±4.83%; sneezing score: 23.08±4.98%). The levels of IL-4 and IL-13 in nasal lavage were diminished remarkably while the level of INF-γ was markedly increased in the BV group. This rendered a significant reduction of the ratio of IL-4/INF-γ. Moreover, a decrease of eosinophils in nasal smear was observed after BV treatment. The BV-induced favorable changes sustained for at least four to eight weeks post BV treatment. Conclusion:Oral administration of BV offers remarkable and sustained efficacy in alleviating AR symptoms and may be considered as an alternative therapeutic strategy for patients with persistent AR. BV acts by improving the overall mucosal immunity via restoring and maintaining the normal Th1/Th2 cytokine balance as an underlying cellular/signaling mechanism.