Abstract: This study explored the effects and probable mechanisms of distribution and redistribution of amino acids in liver of lactating goats fed with different concentrates of forage diet. Six lactating goats fitted with hepatic vascular fistulas were used and they were randomly divided into two groups, in a 2×2 Latin square experiment design with different concentrates to forage ratios of 40∶60 (the control group) and 60∶40 (the high-concentrate group). The experimental interval was 16 weeks. Milk samples were collected and assayed by measuring milk protein content, and plasma samples, including hepatic portal vein, hepatic vein and femoral artery. They were collected via the hepatic vascular fistulas and the contents of free amino acids in plasma were analysed by RP-HPLC. The milk protein content in the high-concentrate group was significantly (P<0.05) lower than that in the low-concentrate group. However, the hepatic portal vein plasma free amino acids content was higher but the contents of hepatic vein and femoral artery plasma free amino acids were lower in the high-concentrate group compared with the low-concentrate group. Thus in the high-concentrate group, the consumption of free amino acids in the liver was more than that in the low-concentrate group, and the content of available free amino acid which transferred into mammary tissue via the femoral artery was less than that in the low-concentrate group. This indicated that long-time feeding with a high-concentrate diet could reduce the milk protein content. Furthermore, it explained that the mechanism of influencing milk protein synthesis was an alteration in concentrations of available free amino acids associated with distribution and redistribution of amino acids in the liver. The amino acids expended in the liver reduced the contents of the mammary gland available amino acids, which are used to synthesize milk protein.