Ivy leaves dry extract is registered as an expectorant in patients with respiratory diseases associated with productive cough. Next to its secretolytical properties, bronchospasmolytical effects are described. However only limited data exist about a possible therapeutical effect in asthmatic patients. In this double blind, placebo-controlled, randomized cross-over study, 30 children (median age 9.07 years (min-max: 6-11)) suffering from partial or uncontrolled mild persistent allergic asthma despite long-term treatment with 400 μg budesonide equivalent were investigated. After a four week run-in period, patients either received ivy leaves dry extract for four weeks in addition to their inhaled corticosteroid therapy or placebo, followed by a wash-out phase before switching to the other treatment arm. Lung function, FeNO, exhaled breath condensate pH and life quality was analyzed after each treatment period. There was a significant improvement of MEF_75-25, MEF ₂₅ and VC after treatment with ivy leaves dry extract (MEF _75-25 change in the mean 0.115 l/s, p = 0.044; MEF₂₅ change in the mean 0.086 l/s, p = 0.041; VC change in the mean 0.052 l, p = 0.044), but not after treatment with placebo. For the primary outcome parameters (relative change of FEV₁ and MEF_75-25 before bronchodilation) no treatment effect could be detected in the cross-over analysis (FEV₁ p = 0.6763 and MEF_75-25 p = 0.6953). This proof-of-concept study indicates that children with mild uncontrolled asthma despite regular inhaled corticosteroid therapy might benefit from an additional therapy with ivy leaves dry extract. However, further studies are needed.