Cholecystokinin octapeptide (CCK8) can exert the immunoregulatory roles through activating immune cell surface receptors such as T lymphocytes, macrophages, dendritic cells, and so on. In this study, we discussed the effects of CCK8 on lipopolysaccharide (LPS)-activated B cells in terms of the expression of co-stimulatory molecules, and the capacity to activate CD4(+) T cells and cytokines production in vitro. The results revealed that B cells expressed two types of CCK receptors; CCK8 inhibited the expression of co-stimulatory molecules such as CD80 and CD86 on LPS-activated B cells, suppressed the proliferation of allogeneic T cells in a dose-dependent manner, and also reduced the secretion of Th1-type cytokine IFN-γ, whereas enhanced the secretion of Th2-type cytokine IL-4 by LPS-activated B cells. Both CCK1R and CCK2R participated in these effects. Taken together, CCK8 is capable of exerting immunomodulatory functions through B cells.