Electrolyte disorder is more common in elderly than that in adult because of the decrease of fluid composition in aging process. The diagnosis and treatment of electrolyte disorder are difficult because of comorbidity in the elderly. The development of electrolyte disorder in the elderly is associated with increased mortality and morbidity in the elderly. Hyponatremia, hypernatremia, hypokalemia, and hyperkalemia are the most common electrolyte disorders in clinical practice. We summarize the symptoms, causes, diagnosis, and treatment of these electrolyte disorders in this article.