This study investigated the effects of different doses of Lactobacillus plantarum on growth performance and serum concentration of amino acids in weaned piglets. A total of 32 piglets [(Yorkshire × Landrace) × Duroc], with an initial BW of 5.6±0.31 kg and weaned at 21d of age, were used for 28d. Pigs were assigned to four experimental treatments with eight replications per treatment and one pig per replication according to a completely randomized design. Dietary treatments consisted of a control group fed with basal alone (T0), Lactobacillus plantarum at 10¹¹ cfu kg^-1 (T1), Lactobacillus plantarum at 5×10¹¹ cfu kg^-1 (T2), and Lactobacillus plantarum at 10×10¹¹ cfu kg^-1 (T3). Supplementation of Lactobacillus plantarum, increased the final BW (P<0.05) and average daily gain (ADG), and decreased (P<0.05) feed:gain ratio and diarrhoea rate compared with the control group (T0). Also, T2 showed the better results on final BW, ADG and diarrhoea rate (P<0.05) compared to other treatments with Lactobacillus plantarum. Likewise, supplementation of Lactobacillus plantarum (mainly the T2) increased (P<0.05) the serum concentrations of lysine, arginine, serine, glutamate, glycine and alanine, and decreased (P<0.05) the concentration of tyrosine; the other amino acids remained similar among the dietary groups. These findings show a beneficial effect of dietary supplementation of Lactobacillus plantarum at 5×10¹¹ cfu kg^-1 on growth performance and the serum concentration of some essentials amino acids and non-essentials in weaned piglets.