In this study, the effects of essential oil mixture, organic acid and essential oil mixture + organic acid supplementation in diets in summer season on egg production traits, egg quality parameters, some digestive system characteristics, some blood parameters and immune response of laying hens were investigated. One hundred ninety two laying hens, 52 wk-old, were divided into 4 treatment groups. There were 48 hens in each treatment group, and each hen was housed individually. The dietary treatments were as follow: 1. basal diet (negative control), 2. basal diet + 36 mg/kg essential oil mixture, 3. basal diet + 2 g/kg organic acid, 4. basal diet + 36 mg/kg essential oil mixture + 2 g/kg organic acid. Laying hens were fed with one of the dietary treatments until 68 wk of age. The treatments had not a significant effect on egg productivity traits but it tends to increase egg weight. However, essential oil mixture supplementation in diet significantly increased albumen height and Haugh unit. No significant differences were observed in serum total cholesterol, glucose and triglyceride levels, and in antibody titer level of Newcastle disease virus (NDV), infectious bronchitis virus (IBV) and infectious bursal disease virus (IBDV) among the treatments, however, supplementing essential oil mixture and organic acid in layer diet tend to improve antibody responses against NDV and IBDV