Background: In December of 2019, Wuhan, a new coronavirus-caused pandemic of atypical pneumonia was reported by China. The World Health Organization (WHO) finally designated this coronavirus and its resulting illness as Coronavirus Disease-2019 (COVID-19). Several biomarkers, such as inflammatory markers C-reactive protein (CRP), D-dimer, ferritin, and Interleukin 6 (IL-6), are related to the development of COVID-19. This study purposed to determine value of Interleukin 6 in disease severity assessment of COVID-19 patients without preexisting pathologies. Methods: This observational comparative cross-sectional study was conducted on 100 participants. They were classified into group A included 25 patients classified as mild or moderate cases, group B included 25 patients classified as severe cases, group C included 25 patients classified as critical ill cases and all was positive PCR COVID-19 and group D (Control Group) included 25 control apparently healthy individuals. History has been taken, clinical examination was done and revealed no comorbidities. Serum Interleukin 6 has been measured in all patients using Enzyme-linked immunosorbent assay (ELISA), laboratory investigations and imaging. Results: It revealed that interleukin-6 was a significant predictor for mild to moderate, severe, and critically ill COVID-19 patients, controlling for age and gender using multinomial logistic regression analysis in predicting COVID-19 severity using interleukin-6. Interleukin-6 can distinguish COVID-19 patients from healthy controls with cutoff point > 3 ng/l, it also can distinguish critically ill patients from other patients with cutoff point > 12 ng/l. Conclusion: Interleukin-6 can significantly predict COVID-19 severity (mild to moderate, severe and critically ill) and mortality.