B lymphocytes are known to play a role in kidney transplantation (KT) outcomes. Here, we evaluated the proportion of B cell subsets before and after KT. Twenty-one patients, who showed stable allograft function without acute rejection in the month following the KT, were included in this study. Peripheral blood samples were obtained from these patients before transplantation as well as 1month after transplantation. Changes in the proportion of B cell subsets after transplantation were investigated using multi-color flow cytometry. The proportion of lymphocytes in the peripheral blood mononuclear cells (PBMCs) and of CD19(+) B cells in the total leukocyte population did not change after KT. Similarly, the proportions of CD19(+)CD24(+) lymphocytes, mature B cells (CD24(Int)CD38(Inter)/CD19(+)), and memory B cells (CD24(+)CD38(-)/CD19(+)) did not change post-KT. However, the proportion of immature B cells (CD24(+)CD38(+)/CD19(+) B cells) decreased significantly after transplantation (P<0.01). The levels of IL-10, and IL-21, and expression of the B cell marker BLNK also decreased significantly after transplantation. Incubation of PBMCs with tacrolimus (0.1, 1, and 10ng/mL) and mycophenolate mofetil (200μg/mL) an immunosuppressant, resulted in significant reduction in the percentage of immature B cells. In contrast, the proportion of memory and mature B cells was not affected. Taken together, these results show that while the total B lymphocyte count and the proportion of memory/mature B cell subsets do not change after KT, the proportion of immature B cells and the associated cytokines that they secrete decrease significantly.