A 93-year-old woman with neurogenic bladder was admitted to our hospital because of impaired consciousness. Her urine culture revealed urease-test-positive Corynebacterium urealyticum. She was diagnosed with hyperammonemia due to an obstructive urinary tract infection that was caused by urease-producing bacteria. The patient showed rapid improvement of impaired consciousness and hyperammonemia after urine analysis. It is necessary to consider obstructive urinary tract infection as a differential diagnosis of hyperammonemia, which commonly occurs in urinary tract infections owing to the presence of urease-producing bacteria. Relief from obstruction is the most important treatment for hyperammonemia caused by this mechanism.