The present study aimed at exploring effect of Urtica dioica on total antıoxidant status (TAS) in rats with experimentally-induced breast cancer. All groups were composed of 15 female rats during 5.5 months experimental period while Group 2 had 13 animals since two rats were dead. When rats were 21 days old, experimental phase was initiated. N-methyl N-nitroso urea (NMU) was used for induction of breast cancer. Control Group (Group 1): fed with basal diet and water, MNU Group (Group 2): 50 mg/kg MNU was injected i.p. and animals were fed with basal diet and water. MNU-administered and Urtica dioica given group (Group 3): In addition to 50 gr/kg Urtica dioica which was given with food, animals in these group also received MNU along with the animals in Group 2. Additionally, 50 gr/L Urtica dioica was boiled, cooled, filtered and used as drinking water. Urtica dioica given group (Group 4): food and drinking water for rats were prepared similar to Group 3. Plasma malondialdehyde (MDA) levels were determined by the method of Satoh and Yagi and TAS levels were determined by a commercial kit. Results were expressed as mean ± SEM. MDA levels in Group 2 was determined to be significantly high compared to Group 4 and Group 1 (p<0.01 and p<0.05, respectively). TAS level of Group 2 was reduced signficantly compared to Group 4 and Group 1 (p<0.05). In conclusion, it is belived that Urtica dioica shows it's protective effect by lowering increased MDA level and increasing TAS.