Peritoneal fibrosis is often provoked by peritoneal dialysis and is an essential precursor condition to the development of encapsulating peritoneal sclerosis. This study aimed to determine the efficacy of a high-density collagen xerogel thread (CXT) for the prevention of peritoneal fibrosis. Female ICR mice received intraperitoneal injections of chlorhexidine gluconate (CG) every other day to induce peritoneal fibrosis. For evaluation, the insertion of CXT or infusion of atelocollagen gel into the peritoneal cavity was conducted on the day before CG injection. For comparison, no collagen treatment after CG injection, and abdominal puncture without CG injection were also performed. Peritoneal fibrosis and inflammation were significantly suppressed by CXT for a long period. CXT prevented mesothelial epithelial-mesenchymal transition, myofibroblast emergence, and inflammatory cell invasion in the peritonitis tissue. In the early phase, atelocollagen gel modulated the expression of the fibrosis-associated protein transforming growth factor (TGF)-β, connective tissue growth factor (CTGF), and CD105 in the peritoneum under CG-induced inflammation, while CXT did not. In contrast, CXT regulated the expression of CTGF and CD105 in the late phase and maintained antimicrobial protein REG3G at the same level as the Sham group in the early and late phases. Although the precise mechanism remains to be clarified, these findings suggest that CXT may have the potential to be developed as a simple therapeutic device to prevent peritoneal fibrosis, a severe complication in patients undergoing long-term peritoneal dialysis.