Hypothyroidism, characterized by insufficient thyroid hormone production, disrupts metabolic processes and impairs reproductive function. It is suggested that oxidative stress plays a key role in mediating the deleterious effects of hypothyroidism on testicular function and because of the antioxidative and anti-inflammatory effects of hydrogen-rich water (HRW), this study aimed to evaluate the effects of HRW on spermatogenesis in rats with hypothyroidism and subclinical hypothyroidism. Thirty male Wistar rats were divided into control, hypothyroidism (hypo), hypo+HRW, subclinical hypothyroidism (sub hypo), and sub hypo+HRW groups. Hypothyroidism was induced using propylthiouracil. After induction of models and four weeks of treatment with HRW (twice daily, drinking water), serum levels of thyroid hormones, LH (luteinizing hormone), FSH (follicle-stimulating hormone), and testosterone were measured. Testicular and epididymal weights, sperm parameters, and oxidative stress markers were evaluated. Hypothyroid rats exhibited significantly lower serum testosterone, with trends toward lower LH, and FSH, compared to controls. HRW treatment significantly increased serum LH and testosterone in the hypothyroid group. Histological analysis revealed reduced epithelial height in seminiferous tubules and lower Sertoli and Leydig cell counts in hypothyroid animals, HRW significantly improved Leydig cell counts and showed a nonsignificant upward trend in Sertoli cells. Sperm count and motility decreased in the hypothyroid group, while sperm motility decreased in both hypothyroid and subclinical hypothyroid groups. HRW administration enhanced these parameters. Additionally, HRW reduced MDA (malondialdehyde) levels and increased SOD (superoxide Dismutase) and catalase activities, indicating improved oxidative stress balance. HRW demonstrates potential as a therapeutic strategy for mitigating reproductive impairments associated with hypothyroidism and subclinical hypothyroidism by restoring oxidative stress balance, improving sperm count and enhancing hormonal profiles.