We studied sex differences lymphocytes subpopulations of peripheral blood in adult C57Bl/6 mice during acute and chronic colitis, induced with 1% DSS. We measured subpopulations of lymphocytes with flow cytometry. We showed that in the control group the female mice had statistically significantly higher values of the relative number of regulatory and cytotoxic T lymphocytes comparing to the males. During acute colitis the females showed an increase in the relative number of Thelpers and a decrease of cytotoxic Tlymphocytes, which reflects the activation of immune response. The males had a decrease in the absolute number of leukocytes, lymphocytes and cytotoxic and regulatory T lymphocytes, probably because of an increase in migration of these cells to the inflammation locus and local lymph nodes. In chronic colitis the females had a decrease in the absolute number of leukocytes, lymphocytes, T helpers, cytotoxic T lymphocytes and B lymphocytes when comparing with acute colitis. During chronic colitis the males had a decrease in the absolute number of T helpers and B lymphocytes but an increase of regulatory T cells in comparison with the control group; in comparison with acute colitis the males with chronic colitis had higher relative and absolute number of regulatory T cells. The increase of T regulatory lymphocytes is due to an increase in their proliferation rate in the thymus and increase of their migration to the inflammatory locus – the colon. Future clinical studies may be based on these results, which show that the treatment of colitis, especially with immunotropic agents, must take sex differences into account.