Hy-line brown commercial layers (32 weeks old) were used to investigate the effects of GABA (gamma-aminobutyric acid) derived from E. coli strains on productivity, egg quality, and blood profile. In total, 288 birds (1946 ± 0.5 g) were fed four different levels of GABA (0, 25, 50, and 100 ppm), in a basal diet based on corn-soybean meal, for five weeks. Egg production, egg weight, and egg mass during weeks 32 to 36 showed significant improvement, as dietary GABA was increased from 0 to 100 ppm (linear, P < 0.05). Additionally, GABA supplementation was associated with increased eggshell breaking strength and albumen height (quadratic and linear, P < 0.05). Blood variables, such as white blood cells, red blood cells, lymphocyte, cortisol, epinephrine, and norepinephrine concentrations, were not influenced by addition of GABA to the diet; however, the haptoglobin concentration decreased significantly (linearly) and the IgG concentration increased (quadratically) in the GABAfed groups (P < 0.05). These results suggest that diets containing GABA may beneficially affect productivity, egg quality, serum haptoglobin, and IgG concentrations in layers.