Major depressive disorder (MDD) is a highly prevalent and debilitating mental illness, which is associated with disorder of gut microbiota. However, few studies focusing on detection of the signatures of bacteria in feces of MDD patients using proteomics approach have been carried out. Here, a comparative metaproteomics analysis on the basis of an isobaric tag for relative and absolute quantification coupled with tandem mass spectrometry was carried out to explore the signature of gut microbiota in patients with MDD. Ten patients (age: 18-56 years, five women) who had MDD and a score over 20 on the Hamilton's Depression Scale and 10 healthy controls (age: 24-65 years, five women) group matched for sex, age, and BMI were enrolled. As a result, 279 significantly differentiated bacterial proteins (P<0.05) were detected and used for further bioinformatic analysis. According to phylogenetic analysis, statistically significant differences were observed for four phyla: Bacteroidetes, Proteobacteria, Firmicutes, Actinobacteria (P<0.05, for each). Abundances of 16 bacterial families were significantly different between the MDD and healthy controls (P<0.05). Furthermore, Cluster of Orthologous Groups analysis and Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that disordered metabolic pathways of bacterial proteins were mainly involved in glucose metabolism and amino acid metabolism. In conclusion, fecal microbiota signatures were altered significantly in MDD patients. Our findings provide a novel insight into the potential connection between gut microbiota and depression.