In this study was aimed to determine the effects of high levels of copper supplementation on some blood values and thyroid hormones in Japanese quails (Coturnix coturnix japonica). It was used totally 64 Japanese quail (one-day-old) as material in the study. Chicks were divided into four groups and they were given 0 mg/kg (control, group I), 100 mg/kg (group II), 250 (group III) and 500 mg/kg (group IV) copper in addition to their concentrate for 40 days. There were no difference hematocrit value, leukocyte number, differential leukocyte number, serum thyroid stimulating hormone (TSH) and free triiodothyronine levels (FT3) between the groups (P > 0.05). Serum copper levels were enhanced in copper supplemented groups (group II, III, IV) (P < 0.05). Copper supplementation to diet was induced to reduce the serum free thyroxine and erythrocyte number in all experimental groups (group II, III, IV) (P < 0.05). Hemoglobin amount were enhanced significantly (P < 0.05) in groups III and IV compared with control group and group II. It was induced to reduce in weight gain the 500 mg/kg Cu supplementation to the diet in compared with other groups (P < 0.05). As a result, the findings obtained from in this study is important that in terms of to reveal effects of excessive copper on thyroid hormones and to be used as a source prospective investigations.