Activin A is a member of transforming growth factor beta (TGF-beta) superfamily, which is also named restrictin-P, and can inhibit the secretion of nitric oxide (NO) and interleukin-1beta (IL-1beta) from LPS-activated mouse macrophages. In this study, the regulation effect and possible mechanism of activin A as an anti-inflammatory factor on lipopolysaccharide (LPS)-activated macrophages were investigated in vitro. It was observed that activin A could not only decrease the secretion of IL-1beta and NO, as well as the mRNA expressions of IL-1beta and iNOS, but also suppress the pinocytosis of mouse macrophage cell line RAW264.7 cells induced by LPS. In addition, activin A could obviously reduce the expressions of CD68 and CD14, as well as Toll-like receptor 4 (TLR4) on RAW264.7 cells induced by LPS, but could not influence the proliferation of RAW264.7 cells. These findings suggest that activin A may play an important down-regulation role in inflammatory factor production and phagocytosis of the activated macrophages via suppressing the maturation of LPS-induced macrophages or LPS-TLR4 signal transduction.