The study aims to investigate the effects of dietary supplementation of thyme on the antioxidant defence mechanisms, immune system, inflammatory cytokines, and production performance and egg quality traits in laying hens. A total of 120, 24-week-old Lohmann-Brown-Classic laying hens were used in this study. The experimental groups were fed on a ration containing 0.1%, 0.5%, and 1% thyme, respectively for 30 days while the control group received the standard chicken feed. Certain parameters such as feed conversion rate (g/g), egg production rate (%), egg mass (g/hen/day) and egg quality were evaluated. Furthermore, differential leukocyte count, heterophil/lymphocyte ratio and certain cytokine levels were assessed. Serum malondialdehyde (MDA), catalase (CAT), superoxide dismutase (SOD), ascorbic acid and glutathione peroxidase (GSH-Px) levels were measured to assess the effects of thyme on the antioxidant defence system. Serum interleukin-4 (IL-4) and GSH-Px activity levels decreased in the 0.1% and 0.5 % thyme groups, respectively compared to those of the control group (p ≤ 0.05). The leukocyte differential counts, as well as heterophil/lymphocyte ratio, did not differ significantly except for a gradual increase in leukocytes and a significant decrease in basophils with the increasing thyme concentration. Likewise, thyme supplementation did not affect performance parameters but exhibited a significant impact on egg yolk color intensity while shell weight, shell thickness, and breaking strength were negatively affected (p ≤ 0.05). It can be deduced that the thyme-supplemented diet did not elicit positive effects on either the antioxidant defence system or the downregulation of inflammation. That the hens experienced no difficulty in consuming the thyme-supplemented diet in the study is considered promising for further studies to be carried out, concerning the effects of higher concentrations of thyme.