Objective To investigate the number and activation status of circulating mucosal associated invariant T (MAIT) cells in patients with sepsis.Methods Flow cytometric method was used to determine the number and percentage of MAIT cells and their expression of activation molecule CD69.Results The circulating MAIT cells dropped significantly at early stage of sepsis in septic patients.The MAIT cells in the sepsis group continued to express high levels of CD69 on day 1 and day 3 after admission to ICU.Conclusions Remarkable decrease of circulating MAIT cells may portend the possibility of sepsis in patients with severe infection.