The possible mechanism of tumor promotion inhibiting activity of garlicextract was studied. The garlic extract could inhibit the cell proliferation of human amnionFL cell in vitro, exerting no influence on the S phase DNA synthesis while exhibitingobvious inhibitory effect on the mitosis of the cells. At suitable concentration, garlic ex-tract could also inhibit the changes of protein kinase C activity induced by tumor promoterTPA, while at higher concentration garlic extract itself could induce changes of proteinkinase C activity mimic to TPA stimulation.