α-diversity was significantly decreased, and the 16S rRNA gene copy numbers tended to increase. Serum IL-6 levels were significantly elevated and positively correlated with the 16S rRNA gene copy number in non-surviving ARDS patients. The copy numbers and relative abundance of Betaproteobacteria were significantly lower in non-survivors. The copy numbers of Staphylococcus, Streptococcus, and Enterobacteriaceae were significantly correlated with serum IL-6 levels in non-survivors. Here, IL6 is linked to acute respiratory distress syndrome.