BACKGROUND Asthma is the most common chronic disease in childhood. Breathing exercise techniques have been widely used by researchers and professionals in the search for complementary therapies for the treatment of asthma. OBJECTIVE To assess the effects of breathing exercises in children with asthma. METHODS We searched for trials in the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, PsycINFO, CINAHL and AMED and handsearched respiratory journals and meeting abstracts. We also consulted trial registers and reference lists of included articles.The literature search was run up to September 2015. METHODS We included randomised controlled trials of breathing exercises alone versus control or breathing exercises as part of a more complex intervention versus control in children with asthma. METHODS Two review authors independently assessed trial quality and extracted data. The primary outcomes were quality of life, asthma symptoms and serious adverse events. The secondary outcomes were reduction in medication usage, number of acute exacerbations, physiological measures (lung function (especially low flow rates) and functional capacity), days off school and adverse events. RESULTS The review included three studies involving 112 participants. All the included studies performed the comparison breathing exercises as part of a more complex intervention versus control. There were no trials comparing breathing exercises alone with control. Asthma severity of participants from the included studies varied. The studies measured: quality of life, asthma symptoms, reduction in medication usage, number of acute exacerbations and lung function. Breathing exercise techniques used by the included studies consisted of lateral costal breathing, diaphragmatic breathing, inspiratory patterns and pursed lips. One study included in the review did not specify the type of breathing exercise used. The control groups received different interventions: one received placebo treatment, one an educational programme and doctor appointments, and one was not described. There were no reported between-group comparisons for any of the primary outcomes. We judged the included studies as having an unclear risk of bias. CONCLUSIONS We could draw no reliable conclusions concerning the use of breathing exercises for children with asthma in clinical practice. The breathing exercises were part of a more comprehensive package of care, and could not be assessed on their own. Moreover, there were methodological differences among the three small included studies and poor reporting of methodological aspects and results in most of the included studies.