Introduction: Ulcerative colitis (UC) is characterized by recurrent episodes of inflammation of the colon; the disease develops as a result of interaction of environmental factors, genetic predisposition and inadequate immune response. Etiology has not yet been clarified. Previous findings confirm that dipeptidyl-peptidase IV (DPP IV/CD26) is a glycoprotein involved in the modulation of immune response through its proteolytic, costimulatory and signaling function. Recent data suggests that the course of the development of UC, nature and intensity of the inflammatory response, depends on the profile of inflammatory cells and mediators, including macrophages which play a key role. Also, studies indicate that a significant role in the development and intensity of inflammation in UC has the phenotype of macrophages which activation is based on the microenvironment conditions. Through its proteolytic activity DPP IV/CD26 acts on a large number of immune cells but its role on the regulation of macrophages polarization has not been clarified yet. Goal: In order to expand the knowledge about the role of DPP IV/CD26 in the modulation of the immune response the main objective of this research was, on an in vivo model of colitis, investigate the influence of the DPP IV/CD26 deficiency on the expression of NF-ĸB and macrophage polarization. Material and Methods: Colitis was induced in C57BL/6 and CD26-defficient (CD26-/-) mice by the dextran sulphate sodium. The health status, changes in body weight, and development of clinical symptoms of colitis were monitored during the experiment, mice were sacrificed on days 3, 7, 10, 15, and 20. Transcriptional expression of the nuclear factor (NF)-κB p65 subunit and macrophage markers of polarization in the colon was done by qPCR, while colon protein expression of NF-ĸB p65 subunit was assessed by immunohistochemical staining Results: Clinical parameters, body mass loss, significant colon shortening along with decrease in the number of the crypts, lead to the conclusion that both mouse strains developed DSS colitis. An increase of myeloperoxidase activity in CD26-deficient mice was more intensive than in C57BL/6 mice, in spite of similar histopathological changes. Furthermore, a significant increase in the mRNA expression of NF-κB p65 subunit of the colon of CD26-deficient mice was determined. A significant increase of hallmarks of M2 macrophages Arg1 and FIZZ1 was determined in CD26-/- mice during development of colitis. Conclusion: This research offers a new insight into the role of DPP IV/CD26 in the process of macrophages polarization and thereby modulating the immune response during the development of colitis.