Conventional treatments for inflammatory bowel disease (IBD) have multiple potential side effects. Therefore, alternative treatments are desperately needed. In the present study, we proposed a new therapeutic tool for the treatment of IBD in murine pre-clinical models by using MSC-Exos. We demonstrated that the infused MSC-Exos are immunotolerated by the host, which is convenient for a future clinical application of MSC-Exos in IBD. To understand the molecular basis mediating the anticolitic benefit of MSC-Exos, we performed proteomic analysis using iTRAQ technology to detect the protein expression profiles in MSC-Exos and the corresponding supernatants from their parent cell MSCs. Proteomic analysis revealed that MSC-Exos were enriched in proteins involved in regulating multiple biological processes associated with the anti-colitic benefit of MSC-Exos. Particularly, metallothionein-2 in MSC-Exos was required for the suppression of inflammatory responses in macrophages. Taken together, MSC-Exos are critical regulators of inflammatory responses and may be promising candidates for IBD treatment.