The effect of dietary supplementation with Agaricus bisporus mushrooms powder (ABP) from by-products on the development, egg production, egg quality, and antioxidant yolk capacity of Japanese laying quail was assessed. A total of 100 female quails 20-week-old were allotted to 5 treatments (5 replications, 4 females each) and received a basal diet supplemented with six graded levels of ABP (0 g/kg, 2.5 g/kg, 5.0 g/kg, 7.5 g/kg and 10.0 g/kg) according to ABP0, ABP25, ABP50, ABP75, and ABP100 groups for 70 days. The results indicated no adverse impact (P>0.05) of dietary ABP on production performance and egg internal quality. A quadratic effect was described for egg-breaking strength (P<0.05) and eggshell thickness (P<0.01), showing the highest values at a dose of 7.5 g/kg ABP. Compared to the control, the 1,1-diphenyl-2-picrylhydrazyl (DPPH) yolk reduction was higher (quadratic) in the 5.0 g/kg ABP diet (P<0.001), while malondialdehyde (MDA) levels decreased linearly in all groups fed with ABP (P<0.001) as compared to the control group. The results suggest that the eggs from ABP quails could have an added value that would improve their marketability. The favourable findings of the current research demonstrate that including mushroom by-products in animal feed could reduce animal feed costs and reduce environmental damage.