Adequate functions of immunoregulation, mediated by regulatory cells such as IL-10 producing CD19+CD38hiCD24hi transitional B cells (Trans), play an important role in control of excessive inflammatory response. Yet, the role of Trans in neonatal sepsis is incompletely understood. We investigated the role of Trans in late-onset sepsis (LOS). We used multicolor flow cytometry to analyse the phenotypes of B cells drawn from a cohort of 16 neonatal late-onset sepsis (LOS) (12 survivors and 4 non-survivors) and 20 healthy neonates over time. Patients undergone a serious decline of lymphocytes at the beginning of sepsis and then noticeable elevation during one week of follow-up had a good prognosis. Intriguingly, peripheral blood B cells, especially Trans, were the marked increase lymphocyte subset and maintained a high level of producing IL-10 during the 7 days of follow-up. The level of IL-10 producing Trans was significantly elevated in peripheral blood of good prognosis newborns with LOS and might contribute to the successful immunoprotective state of the disease. Copyright © 2017. Published by Elsevier B.V.