Objective To investigate the effects of B lymphocyte-induced maturation protein-1 (Blimp-1) on the number and function of splenic lymphocytes. Methods The mice with defective Blimp-1 in T cells were generated by cross-breeding B6.Blimp-1flox/flox mice with B6.Lck-Cre mice. The mononuclear lymphocytes isolated from spleen of T cell conditional Blimp-1 knockout (Blimp-1CKO) mice and wild type (WT) C57/B6 mice were comparatively analyzed. Alterations of CD4+ T and CD8+ T cell subsets, the secretion of cytokines as well as the expression of C-C chemokine receptor type 7 (CCR7) and Sphingosine-1-phosphate receptor 1 (S1P1) in mice from the two groups were analyzed by flow cytometry. The changes of CD19+ B cell subsets were also detected. Results Compared with WT mice, the total numbers of mononuclear cells, T and B lymphocytes were all significantly increased in Blimp-1CKO mice (P<0.05). The absolute numbers of CD4+ T, CD8+ T and CD19+ CD5+ CD1d+ B cells in mice form Blimp-1CKO group were higher than those of the control group (P<0.05), however, no significant differences with the percentages of these cell populations were observed between two groups. Higher numbers and percentages of CD19+ CD5+ B cells were detected in mice from Blimp-1CKO group (P<0.01). The Blimp-1CKO mice showed increased secretion of IFN-γ, TNF-α, IL-17 and IL-2, but decreased expression of CCR7 on CD8+ T cells as compared with WT mice (P<0.05). No significant differences with the changes of S1P1 were found between the two groups. Conclusion Blimp-1 played an important role in the maintenance of number, phenotype and function of T cells. Furthermore, not only T cells but also B cell subsets in mice were affected by the deletion of Blimp-1 in T cells. Key words: B lymphocyte-induced maturation protein-1; T lymphocyte; B lymphocyte