Background: Asthma is an inflammatory airway disorder in which different immune cells in the blood and lungs play a fundamental role. In asthma condition, the airway inflammation accompanied by bronchial smooth muscle spasm cause airway obstruction. A study showed that high concentration of blood serotonin is associated with the intensity and exacerbation of asthma disease. Other studies showed that a subtype of serotonin receptor called 5-Hydroxytriptamine 2A receptor (5- HT2A) can enhance T-cell blastogenesis and production of pro-inflammatory cytokines such as IFNγ. Objective: The objective of this study was to assess the level of 5-HT2A in peripheral blood mononuclear cells (PBMCs) of asthmatic patients. Methods: PBMCs were extracted from blood of 30 patients with asthma and 30 normal people. After synthesizing cDNAs from total mRNAs, real-time PCR was performed to amplify 5-HT2A and β-actin (as an internal control). The expression ratios were analyzed in patients with asthma in comparison with normal group. Results: The results indicated that gene expression is significantly increased in peripheral blood mononuclear cells (PBMCs) of asthma patients in comparison with normal group (P = 0.003). Conclusion: The results of this study can suggest designing a protocol by using of the 5-HT2A receptor expression in PBMCs as a biomarker of asthma, but this requires further studies on a larger number of patients. In addition, the potential role of this receptor in bronchoconstriction can lead us to use its antagonists as a new treatment in asthma.