Background Severe acute respiratory syndrome corona virus 2 (SARS-CoV- 2) infection may trigger a cytokine storm which is characterized by uncontrolled overproduction of proinflammatory cytokines. We aimed to determine associations of circulating levels of inflammatory cytokines with severity of COVID-19. Materials and methods This is a cross-sectional study including 46 severe and 32 mildly symptomatic coronavirus disease 2019 (COVID-19) patients. The serum levels of cytokines, chemokines, and growth factors were determined by using a Bio-Plex Pro™ Human Cytokine Screening Panel (Bio-Rad, Hercules, CA, USA). Results A total of 78 patients with confirmed COVID-19, 54 males and 24 females were included in this study. The mean age was 43.1±13.3 and 58.2±15 in mild and severe patients, respectively. Severe patients were characterized by significant laboratory abnormalities such as increased WBC (p=0.002) and neutrophil counts (p=0.001), higher levels of ALT (p=0.030), AST (p=0.002), LDH (p<0.001), ure (p=0.013), ferritin (p<0.001), D-dimer (p=0.042), CRP (p<0.001) and decreased lymphocyte (p<0.001) and platelet (p=0.045) counts. The levels of IL-6, IL-8, IL-13, TNF-α, IFN-γ, MIP-1β and MCP-1 were increased in the severe group compared to the mild group but only significant differences were observed for IL-6 (p<0.001) and IL-8 (p<0.001) levels. Conclusions Serum IL-6 and IL-8 levels can be used as potential prognostic biomarkers of disease severity in COVID-19 patients.