Abstract Aim of the work: The aim of this study was to assess serum level of stem cell factor in asthmatic patients and its relation to disease severity. Methods: This case control study was carried out on 70 individuals classified into 20 healthy control subjects and 50 asthmatic patients that were admitted in Chest Department, Benha university hospital in the period between March 2013 and December 2014. Asthma diagnosis (history and PFT) and assessment of its severity were conducted according to the guidelines of Global Initiative for Asthma (GINA, 2011). Eosinophil percentage in the sputum of asthmatic patients was done. Measurement of stem cell factor (SCF) in the sera was done by Enzyme-Linked Immunosorbent Assay. Results: Our results found a statistically significant difference (P value < 0.001) between asthmatic patients and control subjects in the mean values of SCF (1192.34 ± 789.89 versus 326.29 ±274.38 respectively). There was a statistically significant difference (P value =0.001) between eosinophilic and non eosinophilic phenotype (1457.77 ±648.83 versus 130.59± 83.27 respectively). There was a statistically significant difference in the level of SCF among different degrees of asthma severity (P =0.001). Also, there was a significant negative correlation (r =
0.288) between SCF levels and FEV1% and significant positive correlation between SCF levels and sputum (r =0.712) and blood (r =0.548) eosinophils% in asthmatic patients.