Monosodium glutamate (MSG) is one of the most extensively used food additives worldwide, which is ingested as part of commercially processed foods. This study aimed to investigate the protective effects of Spirulina (sp) on MSG-induced thyroid disorders in rats. Thirty male albino rats (170 ±10 g) were used in this expeiment. The rats were divided into 5 groups (6 rats in each group), control group (G1), MSG group (G2): treated with MSG (60 mg/k g b.wt./ day), MSG+ 0.5% Sp group (G3), MSG+ 1% Sp group (G4), and MSG+ 2% Sp group (G5). The experiment continued for 28 days. Thyroid gland was examined using biological, biochemical, and histological tests. HPLC analysis of phenolic compounds and chemical composition of Spirulina demonstrated that Spirulina can be considered as a good source of protein, carbohydrates, fibers, minerals (such as iodine), phenolic acids (such as pyrogallol), chlorogenic, catechein and ellagic. In the MSG + SP groups, the biological results indicated that a significant decline in body weight gain (BWG %) and feed intake (FI) were exhibited. Biochemically, a significant decrease in thyroid-stimulating hormone (TSH) and a significant increase in Triiodothyronine (T3) and thyroxine (T4) hormone levels were marketed. As well, a significant increase of antioxidant markers catalase (CAT), glutathione peroxidase (GPx) was noticed in addition to reduced glutathione (GSH) and a decrease in malondialdehyde (MDA) content in thyroid tissues. Histopathological examination of thyroid gland supported these findings and revealed a marked lesion. Therefore, this study reveals that Spirulina  may alleviate MSG-induced  thyroid  disorders  and  play  a  significant  role  in  the regulation of thyroid hormones in rats