This study was conducted to study the effects of  γ-aminobutyric acid (GABA) on growth performance, serum biochemical indices and hormones of HPA (cortisol, corticosterone and adrenocorticotropic hormone), HPT (free triiodothyronine, free thyroxine, triiodothyronine and thyroxine) axis in growing finishing swine. Ninety six (Duroc×Landrace×Yorkshine) growing finishing pigs with an average initial body weight of (43.0±3.2) kg were randomly allocated to four treatments with three replicates in each group and eight pigs in each replicate (1/2 male and female). The treatments included  control group without GABA, 10 mg/kg GABA group (group Ⅰ), 20 mg/kg GABA group (group Ⅱ) and 40 mg/kg  GABA group (group Ⅲ). The experiment lasted for 48 days. At the end of the experiment, the growth performance were determined, and two pigs in every replicate in control group and optimum growth performance group were randomly selected to determine serum biochemical parameters and hormones of HPA and HPT axis. The results showed that different levels of GABA affected growth performance of growing finishing pigs, and 10 mg/kg was the best dosage which significantly increased the average daily gain and feed/gain ratio by 13.08% and 7.81%, respectively (P<0.01). Ten mg/kg GABA increased the serum concentration of triiodothyronine and free triiodothyronine (P<0.05); glutathione peroxidase (GSH-Px) activity was significantly increased (P<0.01); but lactate dehydrogenase (LDH) activity and cortisol, corticosterone and adrenocorticotropic hormone (ACTH) concentrations were decreased(P<0.05). It was concluded that GABA could  improve growth performance of growing finishing pigs by increasing average daily gain and decreasing feed/gain ratio; 10 mg/kg GABA also could enhance antioxidation performance and thyroid function.