The objectives of this study were to investigate the impact of dietary organic mineral mixture (manganese, zinc, and copper) supplementation on reproductive performance, egg quality characteristics, and immune response in laying hens under high ambient temperature. Hens were randomly divided into three treatments: (1) control (basal diet without organic mineral mixture (Mn, Zn, and Cu) supplementation); (2) basal diet + 0.5 g/kg of organic mineral mixture; and (3) basal diet + 1 g/kg of organic mineral mixture from 30 to 38 weeks of age. Hen-day egg production and egg mass were significantly increased by dietary supplementation of 1 g/kg of organic mineral mixture, while feed intake was not affected; therefore, feed conversion ratio (FCR) was significantly improved (P < 0.01). Egg weight, albumen width, shell weight, and shell thickness were significantly increased by the dietary treatments. Serum total cholesterol and glucose were significantly decreased by organic mineral mixture supplementation. Interestingly, yolk contents of total cholesterol and malondialdehyde (MDA) were significantly decreased. Yolk contents of Zn and Cu were significantly increased, while Mn was numerically increased (P > 0.05). Dietary organic mineral mixture supplementation improved the antibody titers against avian influenza H9N1 significantly (P < 0.05) and Newcastle disease virus numerically (P > 0.05) in comparison with the control diet. It might be concluded that the inclusion of organic mineral mixture (Mn, Zn, and Cu) enhanced reproductive performance, shell quality characteristics, plasma profile, yolk mineral concentration, yolk lipid oxidation, and immune response in laying hens under high ambient temperature.