This study aimed to investigate the effects of botanical sanguinarine replacing tryptophan of low protein diets on portal vein plasma flow rate and amino acids metabolism of piglets by testing portral vein plasma flow rate (PVPF), net absorptivity of amino acids and plasma urea nitrogen of piglets. Twelve growing pigs (body wight about 20 kg, Duroc×Landrace ×Large White) were used to install blood intubation (carotid artery, portal vein and mesenteric vein), randomly divided into 4 treatment, each treatment with 3 pigs. Low protein diet was the low-protein group, low protein diet without supplementary tryptophan was the lacking tryptophan group, low protein diet with tryptophan replacement by sanguinarine was the sanguinarine group, normal diet was normal diet group. The results showed as follows: 1) PVPF was on the rise until stabilization in the later period with the feeding time, portal vein blood flow rate within 6 h of the lacking tryptophan group was lower than that of other groups, but no significant difference was observed (P>0.05). 2) The portal vein net absorption levels of lysine, tryptophan and arginine of the lacking tryptophan group was significantly lower than that of other groups (P<0.05), but no significant difference was observed between low-protein group, sanguinarine group and normal diets group (P>0.05). The portal vein net absorption levels of essential amino acid and total amino acid of the lacking tryptophan group was significantly lower than that of other groups (P<0.05), but no significant difference was observed between low-protein group and sanguinarine group (P>0.05). 3) The net absorption of the plasma urea nitrogen were closed in all groups, and no significant difference was observed (P>0.05). In conclusion, the PVPF and net absorptivity of amino acids in portal vein of piglets are affected by feeding low protein diet without adding tryptophan; the PVPF, total amino acids in portal vein and net absorptivity of essential amino acids and total amino acids of piglets are increased by feeding low protein diet with sanguinarine but not trytophan, but the net absorptivity of plasma urea nitrogen is not affected.