This study was conducted to investigate the effects of dietary supplementation with calcium montmorillonite (Ca-MMT) on layers’ oxidation status, immune response, serum biochemistry, performance, and egg quality. A total of four hundred-eighty 75-wk-old laying hens were randomly assigned to 5 treatments with 8 replicates per treatment and 12 hens in each replicate. The hens were fed the basal diet supplemented with 0, 0.3, 0.6, 0.9, or 1.2 g Ca-MMT/kg for 70 d. The Ca-MMT supplementation linearly or quadratically (P < 0.05) increased yolk inde...