Background: SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19), is recognized for the first time in Wuhan, China. The cytokine storm is a known factor causing major clinical symptoms leading to death in COVID-19 patients. Objective: To investigate and compare the serum levels of different cytokines in COVID-19 patients with different clinical severity. Methods: Concentrations of serum cytokines, including IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, TNF-α, IFN-γ, and GM-CSF, were measured in 61 COVID-19 patients and 31 normal controls with ELISA. We investigated the correlation between the levels of these cytokines and clinical severity, CRP level, neutrophil and lymphocyte count in patients with COVID-19. Results: Our data indicated that the levels of IL-1β, IL-2, IL-4, IL-6, IL-8, TNF-α, IFN-γ, and GM-CSF, but not IL-10 were significantly increased in COVID-19 patients compared to normal controls. Statistical analysis showed that the level of IL-1β, IL-2, IL-4, IL-6, IL-8, TNF-α, IFN-γ, and GM-CSF were higher in severe COVID-19 than those of mild cases. The concentrations of all mentioned cytokines were negatively associated with the absolute count of lymphocytes, and positively correlated with the CRP level and the absolute count of neutrophils. Conclusion: The current study suggests that high levels of various cytokines correlate with the disease severity and immunopathogenesis of COVID-19.