Hyperventilation syndrome (HVS) often occurs under stressful conditions, and has been reported during or after anesthesia and operation. HVS, characterized by multiple somatic symptoms and electrolyte imbalances induced by inappropriate hyperventilation, should be managed as an emergency. We report a rare case of HVS during spinal anesthesia. The patient was a previously healthy 51-year-old female without psychogenic conditions. During spinal anesthesia for lower extremity surgery, the patient complained of nausea, headache, paresthesia in the upper extremities and perioral numbness. We found carpal spasm in both hands and flattening of T wave on electrocardiogram (ECG). Emergent arterial blood gas analysis (ABGA) revealed markedly decreased PaCO₂, hypocalcemia and hypokalemia. We managed the patient with verbal sedation, electrolytes replacement therapy and closed mask inhalation. HVS subsided gradually. We conclude that monitoring for possible HVS during anesthesia is very important for patient safety.