Objective To investigate the modulatory effects of mouse spleen-derived mesenchymal stem cells (Sp-MSCs) on the proliferation and activation of T lymphocytes.Methods The mouse Sp-MSCs were isolated from mouse spleens by using explant tissue culture protocol and the cells were induced to differentiate into osteoblasts and adipocytes. The effects of Sp-MSCs on proliferation of activated T lymphocytes were determined by carboxyfluorescein succinimidyl ester (CFSE) staining assay. Furthermore, the effects of Sp-MSCs on lymphocyte transformation test (LTT) and mixed lymphocytes reaction (MLR) were observed, respectively. In addition, the mRNA expression of T cell derived proinflammatory cytokines by Sp-MSCs was detected by quantitative PCR.Results The results of CFSE assay demonstrated that Sp-MSCs suppressed ConA and allogeneic lymphocyte-induced T cell proliferation. Moreover, the Sp-MSCs were capable of suppressing LLT and MLR. Additionally, the results of quantitative PCR revealed that Sp-MSCs significantly suppressed the T cells expressing interferon-γ, tumor necrosis factor-α and interleukine-17A.Conclusions Sp-MSCs are capable of suppressing the proliferation and activation of T lymphocytes as well as the expression of T cell-derived proinflammatory cytokines.