Obesity-associated inflammation with altered immune responses significantly contributes to obesity-related diseases, but the underlying mechanisms are largely unknown. Recent studies have revealed that the gut microbiota also contributes to obesity and the pathology of obesity-related diseases. Mucosal-associated invariant T (MAIT) cells are a unique subpopulation of T cells characterized by the expression of a semi-invariant TCR α chain (Vα19 in mice; Vα7.2 in humans). The development and maturation of MAIT cells require the gut microbiota and antigen-presenting molecule MR1. However, the actual function of MAIT cells has not been well studied. Here we find that obese patients have fewer circulating MAIT cells than age- and gender-matched healthy-weight donors. We also determined the expression levels of the invariant TCR of MAIT cells and classical T cell transcription factors using real-time PCR. We found that Vα7.2 mRNA expression in samples from obese patients was similar to that of healthy donors. Interestingly, mRNA expression of the Vα7.2 TCR was positively correlated with the transcription factor TBX21 (found in T helper 1 cells) and BCL6 (found in follicular helper T cells), regardless of whether the samples were from healthy donors or obese patients. Our study suggests that obesity alters the number of MAIT cells. In addition, the correlation between MAIT cell TCR gene expression and transcription factors of classical effector T cells suggests the existence of transcriptional pathways linking MAIT cells to the function of conventional T cells.