Background: Hypothyroidism, also known as low thyroid hormone, is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone. The aim of this study is to identify the protective effect of flaxseed powder and extract on the chemical and biological properties of rats with hypothyroidism. Methods: 30 male (SPRD) rats were randomly divided into 5 groups of 6 rats each and one of them was kept as a negative (-ve) control group, the rest of rats were administered intraperitoneally with 6-n-propyl-2- thiouracil (PTU, 10 mg/kg) for 15 days to induce hypothyroidism. Then, the groups were divided as follows, group 2 positive control (+ve) fed on basal diet. Treated group (3) fed on basal diet and injection of L-­thyroxin drug at a dose of 0.5 mg/kg, group 4 fed on basal diet and flax seed powder 5g /100g / diet daily and group 5 fed on basal diet and orally dosed of flax seed extract at dose 1ml/kg b.wt / rats daily by stomach tube. Results: The results of the analysis of phenolic compounds showed the highest amount of flaxseed is catechein, gallic, pyrogallol and e-vanillic. The results of the biological evaluation at the end of the experiment showed that the treated groups fed flaxseed powder and extract with levels of thyroid hormones had a significant decrease in the level of (T3) in the blood plasma of the groups affected by thyroid gland. On the other hand, thyroxine (T4) was recorded and also an improvement in the group Treatment with L-thyroxin compared to the control group (+ve). The treated groups showed a significant decrease in serum total cholesterol, triglycerides, LDL cholesterol, ALT, AST, urea, creatinine, uric acid. While body weight gain (BWG), and HDL cholesterol were significantly increased compared to (+ve) group. It showed an increase in the level of thyroid stimulating hormone (TSH) in the blood plasma. Conclusion: Flax seeds powder and extract are readily available supplier of polyphenols with major antioxidants that are functional food components as they influence physiological and biochemical processes, resulting in better health and improved level of thyroid hormone.