Abstract: Objective To investigate the effect of Liangge San, a recipe of traditional Chinese herbal medicine, on lipopolysac-charide (LPS)-induced nuclear factor кB (NF-кB) activation in mouse macrophages cultured in vitro and explore the signal transduction mechanism of the detoxifying effect of Liangge San. Methods The mice were given oral administration of concentrated decoction of Liangge San to obtain the drug-containing serum. Macrophages from mouse abdominal cavity were collected, incubated and subsequently re-incubated with LPS and the prepared serum at different doses. Immunofluorescence method was adopted to examine the expression of NF-кB subunit p65 in the nuclei of the macrophages, and the fluorescence intensity of p65 expression was measured by laser scanning confocal microscope (LSCM). Results The fluorescence intensity of p65 expression in the nuclei of macrophages incubated with LPS for 1 h was significantly increased compared with that in the cells without LPS stimulation and Liangge San serum-treated cells. The fluorescence intensities were significantly decreased in cells treated with the inhibitor TLCK and different doses of Liangge San serum in comparison with those in LPS-stimulated cells. The fluorescence intensities were the lowest in cells treated with TLCK and high-dose Liangge San serum, and the cells treated with moderate and low doses of the serum both showed lower intensity compared with that of LPS-stimulated cells. p65 expression was similar between the macrophages incubated with LPS and those treated with serum that contained no Liangge San. Conclusion Mouse serum containing Liangge San can inhibit LPS-induced p65 expression in mouse macrophages in a dose-dependent manner, which may be one of the signal transduction mechanisms of the detoxifying effect of Liangge San.