MicroRNA (miRNA)-21 and miRNA-155 are important regulators of gene expression of different immunological molecules. This study aimed to investigate the role of miRNA-21 and miRNA-155 as biomarkers in asthma by comparing their serum expression levels in asthmatic patients to those in healthy controls and correlating their levels with serum IL-4. The expression levels of miRNA-21 and miRNA-155 were evaluated by quantitative RT-PCR. Serum levels of IL-4 were determined using ELISA. Asthmatic patients showed significantly higher serum miRNA-21 and miRNA-155 expression levels compared to controls. A statistically significant positive correlation between the expression levels of miRNA-21 and IL-4 serum levels in asthmatic patients was detected. Nonetheless, no correlation was detected between miRNA-155 expression and each of IL-4 and miRNA-21. A receiver operating characteristic curve analysis showed that at a cut-off value of 1.37, the sensitivity of miRNA-21 as an asthma biomarker was 100% and the specificity was 95%. At a cut-off value of 1.96, the sensitivity of miRNA-155 as an asthma biomarker was 100% and the specificity was 100%. It can be concluded that miRNA-21 and miRNA-155 are potential non-invasive biomarkers in the diagnosis of eosinophilic asthma and its response to therapy.