The objective of this experiment was to investigate the effects of crude protein (CP) content with or without Gly supplementation on performance, carcass traits, and litter quality of broiler chickens. One-day-old male broiler chickens were fed isoenergetic diets and were assigned to 5 treatments (12 replicates; 8 broiler chickens/replication). The CP content was different among treatments (starter diet from 22% to 19%, grower diet from 20% to 17%, finisher diet from 18% to 15%). The lowest CP concentration in diets has occurred in treatments 4 and 5, while the CP concentrations in diets in treatments 1, 2, and 3 were greater. Diet from treatment 5 was supplemented with Gly. During the starter period, there were no differences in performance among treatments. In the grower, finisher, and in whole periods, the reduction in CP concentration lowered the broiler chicken performance, regardless of supplementation of Gly in comparison to control treatment in which the protein content has not been decreased (P < 0.05). The reduction in CP in diets also decreased breast muscles, however, the supplementation of Gly decreased fat deposition and increased carcass weight (P < 0.05). The reduction in CP in diets affected improvement litter quality (litter dry matter and N content) (P < 0.05) and also decreasing blood urea N content in litter (P = 0.066). Results indicate that a decrease of CP in diets influenced negatively performance (body weight gain, feed intake, and feed conversion ratio) of broiler chickens (except starter period), percentage of breast muscles, and percentage of abdominal fat. The use of synthetic Gly did not improve broiler chicken performance, however increased carcass quality by reducing fatness.