Rotavirus gastroenteritis a severe viral gastroenteritis that occasionally causes post-renal failure with urinary tract calculus. A 15-month-old boy with rotavirus gastroenteritis suffered from pre-and post-renal dysfunction due to dehydration and urinary obstruction, respectively. Careful evaluations using abdominal ultrasound and cautious fluid replacement with urine alkalization led to an improvement in the pre-and post-renal dysfunction.