Objective We aimed to investigate the effects of flaxseed, which is widely used due to its healing effects, on the kidney tissue when the daily recommended dose is exceeded. Material and Methods We divided the male Wistar Albino rats into four groups of eight, namely the control, OD-1 (1.4 mg/ kg/d), OD-2 (2.8 mg/kg/d), and OD-3 (5.6 mg/kg/d) groups. Ground flaxseed was administered to each overdose group by oral gavage for 7 days. At the end of the experiment, blood and kidney samples were collected. Blood samples were centrifuged and serum was separated for renal function analyses. The half of the kidney samples were stored at -20 °C until biochemical analyses and we fixed the remaining tissues with 10% buffered formalin for histopathological analysis. Results Serum urea and BUN levels were significantly increased in all overdose groups compared to the control group (for all p˂0.05). TAS levels significantly decreased in the OD-3 group compared to the control (p=0.044). There was an increase renal TOS levels in all overdose groups compared to the control and also, OSI level of the OD-3 group significantly increased compared to the control (p=0.016). While histopathological changes were not observed in OD-1 and OD-2 groups compared to the control group, there were non-significant histopathological changes in OD-3 group. Conclusion It was concluded that the use of flaxseed above the recommended daily dose can pose a threat to kidney tissue. So, while being used for its benefit, in order not to be exposed to its toxic effects, overuse and longterm use should be avoided.