It was aimed to investigate the radioprotective activity of Urtica dioica L. seed extract (UDSE) in the vvho le blood and liver of radiation-administered rats, both biochemically and immunohistochemically. 32 rats were divided into 4 groups (n:8). Control group (C): no administration for 10 days. Radiation group (IR): fed pellets for 10 days after exposure to radiation. Radiation + UDSE (IR+UDSE) group: exposed to radiation and fed UDSE for 10 days. UDSE group (UDSE): fed UDSE for 10 days. Radiation (5Gy ) was given as a single fraction. 8-hydroxy-2-deoxyguanosine (8-OHdG) and deoxyguanosine (dG) levels were analyzed by biochemical method and glutathione peroxidase 1 (GPx-1) analyses were performed by immunohistochemical method in the liver and blood tissues of the rats. The increased 8-OHdG rates and decreased GPx-1 immunorcactivity was observed in the IR group. Those parameters were ameliorated in the IR+UDSE group when compared to the IR group. UDSE is likely to be a valuable radioprotector against the harmful effects of radiation.