Asthma is one of the most common chronic inflammatory disorders in children. Nonadherence to medical therapy is a major cause of poor clinical outcome the objective of this study was evaluating factors, which are resulted in nonadherence to medical therapy in children with asthma.In this descriptive study, 150 children with asthma and nonadherent to medication therapy were enrolled. General information and probable causes of nonadherence were recorded in self-report questionnaire and data were analyzed. In our study, 57.3% of children were male. Approximately 43%of children belonged to age group 6-9 years old. Prevalence of probable causes of nonadherence to treatment were concern about treatment expenses(34.7%) ,fear of cardiac complications(34.7%), concern about drug dependency(38.7%), belief to growth inhibition(30.7%) and fear of osteopenia (32%). There was statistically significant reverse association between treatment with multi-drug regimens and concern about bone mineral abnormalities, cardiac complications and drug dependency (p=0.0001, 0.014 and 0.012 respectively). In addition, there was a significant association between mild asthma and fear about drug dependency (p=0.001).According to our results, factors such as prolonged duration of treatment, various therapeutic regimens, and receiving multiple drugs before diagnosis of asthma pose the highest frequencies for nonadherence.