Probiotic bacteria have been suggested to stimulate the host immune system. In this study we evaluated the immunomodulatory effects of probiotic Bacillus cereus var. toyoi on the systemic immunity of piglets. A pool of 70 piglets was divided into a probiotic or control group. We determined the ratios of peripheral blood mononuclear cell (PBMC) subsets and measured proliferative responses and cytokine production of PBMCs and effects on vaccination responses. Blood samples of probiotic-treated piglets showed a significantly lower frequency of CD8high/CD3+ T cells and CD8low/CD3+ T cells and a significant higher CD4+/CD8+ ratio. IL-4 and IFN-γ production of polyclonally stimulated PBMCs was on average higher in the probiotic group. Specific proliferative responses of PBMCs to Influenza vaccination antigens were significantly higher and antibody titers against H3N2 Influenza and Mycoplasma vaccination antigens were on average higher in the probiotic group. In conclusion, B. cereus var. toyoi therefore alters the immune status of piglets as indicated by changes in the ratios as well as functionalities of systemic immune cell populations.