The effect of administration of daidzein (5.0ppm) during late pregnancy on the immune function of sows and neonate piglets as well as on the levels of growth hormone (GH), prolactin (PRL) and somatostain (SS) in serum and colostrum of sows were studied. These results showed: 1) The concentration of antibody to swine fever virus vaccine and hemolysin in sow serum and colostrum were significantly enhanced, suggesting that both the systemic and mammary gland humoral immune functions in sows was notably enhanced. 2) The concentration of antibodies in neonate piglets from sows markdedly increased through colostrum absorption. 3) GH and PRL levels of sow serum and colostrum were strikingly enhanced, but the serum SS level was apparently lower than that of the control animals. It seems likely that the mechanism of daidzein regulated immune function is involved in decreasing the SS level, and increasing both the GH and PRL levels.