Background Atopy is a state of allergy to common antigens and is founded on an immune disturbance of exuberant Th2 activity and IgE production. There is also epidemiological and experimental evidence that exposure to mycobacteria has the potential to suppress the development of asthma or atopy. Since Th1 and Th2 immune mechanisms are significantly antagonistic, it is hypothesized that mycobacterial exposure may moderate atopic disease by modification of immune responses. Methods One hundred and twenty mild to moderate persistent asthmatics accompanied with allergic rhinitis were randomly divided into four groups with one injection every other day for 18 times for group A with 1 ml of normal saline, B with 0.5 mg of Bacillus Calmette-Guérin polysaccharide nucleotide (BCG-PSN) and C with 1 mg of BCG-PSN, 36 times for group D with 0.5 mg of BCG-PSN. Markers for the severity of asthma and rhinitis including the amount of inhaled corticosteriod, bronchodilator and oral H1 blocker-loratidine being used to obtain optimal symptomatic control, symptom scores of asthma and allergic rhinitis, peak expiratory flow (PEF), histamine provocative dose that produces at least a 20% change in forced expiratory volume with in 1 second (PD20-FEV1), blood IgE levels as well as dermatophagoides pteronysinus (DP) and dermatophagoides farinae (DF) skin prick test were measured every visit for 6 months. Results There were no differences for symptom scores of asthma, daily use of bronchodilator, PEF, PD20-FEV1, blood IgE as well as DF and DP skin prick test among the four groups. Score for allergic rhinitis decreased significantly in groups B, C and D on day 36 and 72 as compared with group A (P<0.05). Score for allergic rhinitis increased after day 72 in group B and C while it was significantly lower in group D (P<0.05). The patients in group D used less amount of inhaled beclomethosone than other groups (P<0.05) from day 72 after the treatment to day 180. Oral loratadine consumption in groups B, C and D was significantly less on day 36 and 72 as compared with their baseline and group A after the treatment (P<0.05). Group D maintained significantly lower dosage of oral loratadine until day 150 comparing with its baseline and group A. Conclusions BCG-PSN has a symptomatic effect on allergic rhinitis. BCG-PSN may reduce the dosage of non-sedative H1 blocker loratadine as well as the dosage of inhaled beclomethosone in the treatment of mild to moderate asthma and allergic rhinitis.