Significance The COVID-19 pandemic caused by SARS-CoV-2 infection has led to more than 840,000 deaths worldwide as of August 31, 2020. Unfortunately, no licensed vaccine or specific treatment is available right now. Herein, we report a decoy nanoparticle against COVID-19. The decoy nanoparticles were constructed by fusing cell membrane nanovesicles derived from genetically engineered cells, which stably express SARS-CoV-2 receptor ACE2, and human monocytes, which display abundant cytokine receptors. By competing with host cells, these nanodecoys efficiently adsorb viruses and inflammatory cytokines such as IL-6 and GM-CSF. These two functionalities allow effective intervention of viral infection and its associated immune disorder, presenting a promising therapeutic strategy for COVID-19 and other potential epidemics.