This study evaluated the effect of thyme (Thymus vulgaris L.) on productive performance, egg quality, blood profile, immune function and antioxidant enzyme activity in laying hens. A total of 96 thirty-six-week-old laying hens were assigned to a basal control diet or a diet supplemented with 3, 6, or 9 g · kg^–1 of thyme fed from 36 to 52 weeks of age. Hens were divided into four equal groups replicated six times with four hens per replicate. No significant differences were observed among the dietary treatments in body weight change, feed consumption, or feed conversion ratio. Supplementation of thyme up to 6 g · kg^–1 in the diet led to an increase in egg weight compared with the basal diet. Egg number was not (P > 0.05) influenced by thyme supplementation, except from 36 to 40 weeks of age. Birds fed diets with 3 or 6 g · kg–1 of thyme had greater (P < 0.05) egg mass than those fed the unsupplemented diet or that with 9 g · kg^–1 of thyme. Dietary supplementation with thyme exhibited a significantly positive effect on parameters related to immunity and lipid profile. Serum superoxide dismutase activity and reduced glutathione concentration were significantly increased in groups fed diets with thyme (P = 0.010 and P < 0.001, respectively). The malondialdehyde concentration was decreased (P = 0.048) in experimental groups in comparison with the control. In conclusion, thyme supplemented up to 9 g · kg^–1 diet can be used as an effective feed additive to improve productive performance, blood profile and antioxidant enzyme activities in laying hens.