This study aimed to evaluate the effect of flavonoid supplementation to a low-protein diet (LCP) on growth performance, nutrient digestibility, excreta bacterial count, and excreta gas emission of broilers. In total, 800 one-day-old Ross 308 broilers (BW; 42.90±1.43g) were randomly sorted into one of the 4 dietary treatments (10 pens/treatment; 20 birds/pen). Treatment diets were high-protein diet (HCP), basal diet; LCP, basal diet−2.5% protein; TRT1, LCP+0.025% quercetin; and TRT2, LCP+0.050% quercetin. Experimental diets were provided to broilers from days8 to 35. HCP, TRT1, and TRT2 showed higher body weight gain (BWG) than the LCP group during days8–21 and in the overall experiment. However, feed conversion ratio of the HCP group was improved than that of the LCP group during days8–21 and in the overall period. The increasing level of quercetin supplementations brought a linear increase in BWG. Lactobacillus, Escherichia coli, and Salmonella counts in excreta samples of the experimental groups showed no significant difference. Flavonoid supplementation (0.050%) reduced drip loss in breast muscle more than that in the LCP group and showed a linear reduction. Through improved digestion, quercetin addition to an LCP reversed the BWG.