This study was to determine the effects of supplemental AA in low-protein diets on tight junction and AA transporters in the small intestine of growing pigs. 72 pigs (19.7 ± 1.1 kg, 36 barrows and 36 gilts) were allotted to 3 treatments with 8 pens per treatment (3 pigs per pen, 4 barrow pens and 4 gilt pens) using sex and initial BW as blocks: NC (supplemental Lys, Met, and Thr at 18% CP), PC (supplemental Lys, Met, and Thr at 16% CP), and PCT (PC + 0.05% Trp). The NC and PC diets had AA to meet the NRC 2012 requirements (0.98% Lys, 0.55% Met + Cys and 0.59% Thr) whereas PCT diet had additional 0.05% Trp exceeding the requirement. After 4 wk feeding, 24 pigs (1 pig per pen with median BW) were euthanized to obtain duodenum and jejunum to quantify tight junction proteins (claudin-1, occludin-1, and ZO-1) and jejunum to quantify mRNA of AA transporters (CAT-1, b^0,+AT, rBAT, y⁺LAT, 4F2hc, and B⁰AT). Tight junction proteins were separated by Western blot and bands densities were measured. The mRNA of AA transporters was quantified by a real-time PCR. Data were analyzed using the Mixed procedure of SAS. Treatment and sex were the fixed effects and initial BW was a random effect. Pigs in PCT had increased (P < 0.05) claudin-1 in duodenum and jejunum compared with pigs in NC and PC. No difference in ZO-1 in duodenum and jejunum was detected among treatments. Pigs in PC had decreased (P < 0.05, 39.3%) occludin-1 in duodenum compared with pigs in NC. There was no difference in occludin-1 between PC and PCT. Pigs in PC and PCT had increased (P < 0.05) mRNA concentrations of CAT-1 (2.29 and 1.92 fold), 4F2hc (2.76 and 2.45 fold), and B⁰AT (2.12 and 2.26 fold, respectively) compared with pigs in NC. Collectively, use of supplemental amino acids (Lys, Met, Thr, and Trp) in low protein diet to meet the NRC 2012 requirements could increase AA transporters in jejunum and additional 0.05% Trp exceeding the NRC 2012 requirements enhanced intestinal tight junction.