Finding an applicable clinical biomarker in body fluids can be useful in asthma management.  This study was conducted to support the investigations of probable immunological changes in asthmatic patients that may be useful therapeutic indicators. 61 matching patients and 23 apparently healthy individuals were included. Significant elevation in the level of eosinophil cationic protein (ECP) in asthmatics was found as compared with healthy controls, so as among asthma severity categories. The receiver operating characteristic curve analysis determined 29 ng/ml of serum ECP as the typical cut-off value of significant denotation for differentiation between asthmatic patients and healthy individuals, significant positive linear correlation between both ECP level and also ECP/Eosinophil ratio with clinically estimated asthma severity were observed. The median of serum total IgE and rate of 100 IU/ml overlapped serum total IgE individuals were significantly higher in asthmatics than healthy controls and so as among asthma severity categories, whereas no significant correlation between total serum IgE level and asthma severity was found. According to the results, determination of serum ECP can be considered as a diagnostic tool to distinguish asthma cases, besides it reflects the severity of the disease significantly, whereas calculation of ECP/Eo ratio may be an effective marker in reflecting asthma severity and the activity of eosinophils during the inflammation which may be useful in asthma control and in the assessment of  the disease severity as well as the response to anti-inflammatory therapy, but it has no benefit for diagnosing asthma as no significant differences were recorded between asthmatics and healthy controls.