Abstract Background: Hyperthyroidism was one of the most com-mon endocrine disorders. Urinary tract dysfunctions were common symptoms in hyperthyroid patients. Folic acid is affected by Thyroid dysfunction as hyperthyroidism is asso-ciated with subclinical deficiency and depletion of folate stores. Aim of Study: To study the morphometric and the in-vitro contractility changes of the urinary bladder in hyperthyroid rats, and the protective effect of folic acid and its possible mechanisms. Material and Methods: Forty male albino rats divided into four groups: Control, hyperthyroid, folic and (hyperthyroid + folic) groups. TSH, T3, T4, MDA & PGE2 were measured. Rats were then sacrificed. The weight, morphometric changes and phasic activity of the urinary bladder were assayed. Results: Hyperthyroid group significantly decreased TSH and increased T3 (Triiodothyronine), T4 (thyroxine), MDA (malondialdehyde) and PGE2 (prostaglandin E2), bladder weight, wall, and lumen areas with unchanged wall thickness, and increased smooth muscle and urothelium areas with unchanged collagen area and increase the contractile response of the urinary bladder strips to acetylcholine when compared to the control group. Co-administration of folic acid to hyper-thyroid rats significantly increased TSH and decreased T3, T4, MDA and PGE2, bladder weight, wall, lumen areas, smooth muscle, urothelium areas and the contractile response of the urinary bladder strips to acetylcholine when compared to the hyperthyroid group. Conclusions: Folic acid protects against enhanced bladder contractility and bladder remodeling in hyperthyroid rats possibly through ameliorating the increased thyroid hormones levels, anti-oxidative, and anti-inflammatory properties.