Quercetin was fed to groups of broiler chickens at concentrations of 200, 400, and 800 ppm, and a control group was supplemented with a basal diet. Results revealed that quercetin dietary supplementation numerically improved the growth performance traits and significantly increased (p < 0.05) the European production efficiency factor (EPEF) in the 200 ppm group. The total coliforms and Clostridium perfringens were decreased (p < 0.05) in quercetin-supplemented groups. Conversely, Lactobacillus counts were increased (p < 0.05), due to improvement of the gut microbiota environment in quercetin-supplemented groups. Moreover, the mRNA expression of intestinal Cu/Zn-superoxide dismutase (SOD1), glutathione peroxidase (GSH-Px) and nutritional transporters, including glucose transporter 2 (GLUT2), peptide transporter 1 (PEPT1), and fatty acid synthase (FAS) genes, were significantly upregulated in quercetin-supplemented groups. Quercetin enhanced intestinal morphometry. We can suggest quercetin supplementation in broiler chickens by levels between 200 and 400 ppm to enhance their development and gut environment.