OBJECTIVE： To explore the clinical efficacy and safety of alfacalcidol in the adjuvant treatment of bronchiolitis in children. METHODS： Data of 156 children with bronchiolitis were retrospectively collected and divided into observation group （78 cases） and control group （78 cases） by different medication. All children received oxygen inhalation， relieving asthma， antiviral and other conventional treatment， then control group inhaled Budesonide suspension 0.5-1.0 mg + Salbutamol aerosol 0.25 mL for atomization， bid， 10 min every times， 7-d was a course. Observation group additionally given Alfacalcidol soft capsule 0.010-0.015 μg/（kg·d）， 3 times a week， 3-month was a course. They were treated for 3 months. Clinical efficacy， improvement time of clinical symptoms and signs， levels of 25-（OH）D3 and serum LEP， IgA， IgG， IgM and IgE before and after treatment， and the incidence of adverse reactions in 2 groups were observed and compared. RESULTS： The total effective rate in observation group was significantly higher than control group， improvement time of cough， asthma， wheezing and moist rale were significantly shorter than control group with statistical significansce （P＜0.05） after 7-d treatment； after 3-month treatment，25-（OH）D3， IgA and IgG levels were significantly higher than before， and observation group was higher than control group， LEP and IgE levels were significantly lower than before， and observation group was lower than control group， with statistical significances （P＜0.05）. There was no significantly difference of the level of IgM in 2 groups before and after treatment. And there were no severe adverse reactions in 2 groups. CONCLUSIONS： Based on conventional treatment， alfacalcidol shows good efficacy in the adjuvant treatment of bronchiolitis in children， which can obviously enhance immune function， reduce serum LEP level， then shorten remission time of clinical symptoms and signs， with less adverse reactions and good safety.