Heat-inactivated microorganisms are a typical class of postbiotics with promising potential health effects, as they contain various physiologically active components. Dietary supplementation withCompanilactobacillus crustorumMN047 (CC) has been shown to have the potential to alleviate ulcerative colitis (UC). However, it is unclear whether the UC-relieving effect of this strain is partly attributed to its bacterial composition. Therefore, the interventional effects of heat-inactivated CC (HICC) on UC mice were explored. The results showed that the administration of HICC significantly ameliorated the UC-related pathological parameters by (1) alleviating the pathologic lesions of UC (e.g., preventing the increase in disease activity index and the shortening of colon length); (2) ameliorating the colonic inflammation (e.g., inhibiting the expressions of chemokines and pro-inflammatory cytokines, such asCxcl1,Cxcl5,Ccl7,TNF-α,IL-1β,IL-6, andMCP-1; (3) attenuating the oxidative damage (e.g., suppressing the increase in myeloperoxidase and malondialdehyde); (4) mitigating the damage of gut barrier (e.g., promoting colonic occludin, ZO-1, and claudin levels); and (5) modulating gut microbiota structure (e.g., increasing the relative abundance of potential probiotics, such asAkkermansiaandLactobacillus). In conclusion, our study suggested that HICC can be effective in preventing UC and has the potential as a dietary supplement to intervene in UC.