The fruit Punica granatum L. has been used for years in traditional medicine owing to the presence of several phytobiotics with antimicrobial and immunomodulatory properties. This study investigated the effects of dietary supplementation with Punica granatum L. by-products (PGB) on performance, immunity, intestinal and excreta microflora, and odorous gas emissions from excreta of broiler chickens. Three experimental diets containing 0, 0.5 and 1.0% PGB were fed to 240 one-day-old broiler chicks until 35 days. Dietary PGB linearly reduced the average daily feed intake and feed conversion ratio of broilers. Supplementation with 1% PGB led to a linear increase in the relative weight of the spleen and bursa of Fabricius. The concentration of serum IgA and IgG increased linearly in response to dietary PGB. In the ileal digesta, the concentration of Saccharomyces cerevisiae increased linearly and quadratically in response to dietary PGB. Moreover, dietary PGB led to a linear decrease in Escherichia coli and Salmonella spp. alongside reducing the pH of the ileal digesta. In the cecal digesta, the concentration of Bacillus bacteria increased linearly in response to both levels of dietary PGB, while the concentrations of E. coli and Salmonella decreased when the diet was supplemented with 1% PGB, as did cecal pH. At 35 day, both levels of PGB increased the concentration of fecal Bacillus, whereas only 1% PGB increased the concentration of S. cerevisiae at 21 day. Increasing levels of PGB induce a linear reduction in fecal E. coli at 21 and 35 day, whereas Salmonella only at 21 day. Regarding the average of 48 h, dietary PGB effectively reduced the emissions of ammonia and methanethiol from broiler excreta. In conclusion, the results suggest that, dietary PGB improved immunity and the intestinal microbial ecosystem of broilers along with reduced odorous gas emissions from excreta.