The objective of this study was to determine the response of broiler chickens to different dietary sodium (Na) levels. The experiment was performed on 432 male Ross 308 chickens, kept in three-tier battery cages, each with a floor area of 0.5 m². The chickens were divided into six experimental groups of eight replicates, each of nine birds. Six experimental diets were prepared: a basal diet without additional Na source and diets supplemented with NaCl in the amount of 0.52, 1.03, 1.54, 2.05 and 2.54 g/kg in the starter period (1-14 days) and 1.27, 2.54, 3.82, 5.09 and 6.36 g/kg in the grower period (15-35 days). The dietary Na, Cl and K content was 0.22-2.61, 1.11-4.81 and 8.76-9.61 g/kg, respectively. Dietary electrolyte balance (DEB), defined as Na⁺ + K⁺ - Cl^-, averaged 210 mEq/kg in all diets. The Na content of basal diets was very low (0.33 g/kg in starter diets and 0.22 g/kg in grower diets). It inhibited the growth of broilers despite a high DEB resulting from a high K content (about 9 g/kg). The addition of NaCl to starter diets significantly increased the body weight (BW) of chickens, but only to the amount of 1.1 g Na per kg feed. The addition of 2.54 g NaCl per kg grower diets increased the Na and Cl content of the diet to 1.16 g/kg and 2.68 g/kg, respectively, leading to a significant improvement in overall production results, slaughter value and tibia mineralization, without negative effect on excreta moisture. A further increase in the Na content of grower diets (to 1.69, 2.18 and 2.61 g/kg, respectively), accompanied by an increase in Cl concentrations (to 3.38, 4.11 and 4.81 g/kg, respectively) did not increase the BW of chickens, feed conversion efficiency and slaughter value, while it increased excreta moisture and decreased parameters characterizing the mineralization and elasticity of the tibia in birds fed a diet with the highest Na content (2.61 g/kg). As compared to the group fed the basal diet, the medium and highest Na dosages significantly decreased pH and dry matter concentration of small intestine contents; the treatment with the highest dietary Na levels stimulated bacterial β-glucosidase and β-glucuronidase, yet it did not increase the caecal short-chain fatty acids concentration.