Background: Lithium-containing drugs are the recommended treatment for bipolar disorder. Aim of the work: The current study aimed to assess the toxic effects of lithium carbonate on the kidneys and parathyroid glands and evaluate the possible protective effect of chitosan. Material and Methods: Sixty adult male albino rats were divided into six groups of ten rats each. Group I (negative control group). Group II: 200 mg/kg/day of chitosan was administered orally. Group III: 25 mg/kg/day of lithium carbonate was administered orally. Group IV: Rats were given chitosan (200 mg/kg/day) and lithium carbonate (25 mg/kg/day) orally. Group V: 50 mg/kg/day of lithium carbonate was administered orally. Group VI: Rats were given chitosan (200 mg/kg/day) and lithium carbonate (50 mg/kg/day) orally. After 4 weeks, the rats were sacrificed after being anaesthetized. Blood samples were collected. Kidneys were dissected for histopathological and immunohistochemical studies. Results: Lithium toxicity induced a significant statistical increase in the serum levels of urea, creatinine, parathormone hormone, and calcium. Also, there was a significant statistical decrease in TAC. The co-administration of chitosan with lithium resulted in an improvement in the biochemical parameters. Some histopathological changes were observed in the kidneys of lithium-treated rats. These changes were less evident when chitosan was co-administered. There was high positive TNFα expression in the kidneys of lithium-treated rats. Less TNFα expression was observed when chitosan was co-administered. Conclusion: Lithium carbonate subacute toxicity induced renal damage, hyperparathyroidism and hypercalcemia. The use of chitosan can reduce the negative effects of lithium due to its antioxidant and anti-inflammatory properties.