¹Department of Animal Nutrition and Nutritional Diseases, Afyon Kocatepe University, TR- 03200 Afyonkarahisar - TURKEY DOI : 10.9775/kvfd.2019.22058 The aim of the present study was to evaluate the effects of myrtle plant extract (MPE) on performance, some blood parameters, egg quality and immune response of older laying hens. A total of 192 laying hens (67 weeks old; initial body weight 1.63±0.17 kg) were used in this study. The MPE was added to the water of the experimental groups (0%, 2.5%, 5.0%, or 10%) for 8 weeks. Liquid chromatography analyses showed that myricetin was the predominant active ingredient (15.34 mg/L) in MPE. In treatment groups, feed consumption, egg mass (P<0.05), egg production (P<0.01) increased (10% MPE) and water consumption ascended (5% MPE) compared to the control birds. Feed conversion ratio did not change. In 2.5% MPE group, greater egg weight (P<0.001) and darker egg yolk (P<0.01) were observed than the control birds. Regarding immunity, the 5% Myrtus group produced higher neutrophil and large amounts of IgG (P<0.05) indicating that significant results were also observed in the immunological response of laying hens vaccinated against the Newcastle virus. Serum alanine aminotransferase level increased (P<0.05) in treatment groups whereas serum glucose levels decreased significantly (P<0.01). Other than that, none of the blood parameters changed. It is concluded that Myrtus communis L. plant extract showed positive effects on the egg yolk, some performance parameters and immune system of older laying hens without any adverse effects on egg traits. Keywords : Common myrtle, Antibody response, Immunonutrition, Serum profile, Aged hens