BACKGROUND: Probiotics may prevent the allergic response’s development due to their anti-inflammatory and immunomodulatory effects. The aim of this study is to determine if the prophylactic treatment with a mixture of Bifidobacterium animalis subsp. Lactis BB12 and Enterococcus faecium L3, would reduce symptoms and need for drug use in children with allergic rhinitis (AR). METHODS: The study included 250 children aged from 6 to 17 years, affected by AR. Patients were randomly assigned to the intervention group (117) or to the placebo group (86). Patients of the intervention group, in addition to conventional therapy (local corticosteroids and/or antihistamines), were treated, in the 3 months preceding the development of AR symptoms, with a daily oral administration of a probiotic mixture containing the Bifidobacterium animalis subsp Lactis BB12 DSM 15954 and the Enterococcus faecium L3 LMG P-27496 strain. Nasal Symptoms Score(NSS) was used to evaluate AR severity before and after the treatment with probiotics or placebo. RESULTS: 96% of the patients in the intervention group showed a significant decrease in their NSS after the probiotic treatment as well as a decrease in the intake of pharmacological therapy. GPower software was used to calculate the test power. Given the probability of error α = 0.05, the total sample size n = 117 and the effect size ρ = 2.0651316, the power of the test is 1 - β = 1. CONCLUSIONS: When administered as a prophylactic treatment the mixture of BB12 and L3 statistically decrease signs and symptoms of AR and reduces significantly the need of drugs.