Background: MicroRNAs (miRNAs) are emerging gene expression regulators and their expression has been linked to various biological processes. However, the role of miRNAs in the regulation of allergic inflammatory disease still not clearly understood. Aim: Our study was designed to investigate circulating miR-155 and Let-7a expression levels in the plasma of asthmatic children and healthy controls. Also, to correlate their expression levels to degree of severity of asthma as well as to IL-13 level and lung function parameters. Method: Our study included 100 asthmatic children and 100 healthy children as control group. Plasma miR-155 and Let-7a expression levels were measured by quantitative real-time polymerase chain reaction (qRT-PCR). Results: MicroRNA-155 expression was significantly increased in the plasma of asthmatic children than in control children. While, Let-7a expression was significantly lower in asthmatics than in control children. The relative levels of miR-155 and Let-7a were associated with degree of asthma severity. Receiver operating characteristic (ROC) curve analysis demonstrated that the levels of miR-155 and Let-7a were helpful for diagnosis of childhood asthma (AUC were 0.91 and 0.92, respectively), and in prediction of the severity of disease (AUC were 0.83 and 0.80, respectively). Plasma miRNA-155 was correlated positively with Il-13 levels and correlated negatively with FEV1and FVC. While, Let-7a was correlated negatively with Il-13 and correlated positively with FEV1 and FVC. Conclusion: MicroRNA-155 and let-7a could be used as serological non-invasive biomarkers for diagnosis of asthma and degree of severity. Our results could be used for exploring the pathogenesis of asthma and help in selecting promising therapeutic modalities