We report on a case demonstrating unilateral Horner's syndrome (HS) after lumbar epidural obstetric anesthesia. A healthy, 32-year-old woman with a breech presentation was scheduled for an elective Cesarean section. The patient had normal vital signs throughout the surgical procedure. The operation lasted for 50 min. In the recovery room, she complained of left nasal stuffiness, left cheek numbness, and heaviness in her left eye. Meanwhile, left nipple sensory loss was noted during baby suckling training. On physical examination, her left eyelid was droopy along with left-side ptosis and facial flushing. Reduced sensation over the left hemifacial region and upper arm was also noted, which resolved completely over the next 110 min. A diagnosis of unilateral HS was then made. Although typically a benign side effect which often spontaneously resolves, HS is likely to cause anxiety in both the patient and the doctor. Prompt recognition of this syndrome and determination of its cause from lumbar epidural anesthesia can prevent unnecessary and potentially dangerous diagnostic workup and can reassure both patients and clinicians. The patient was discharged from the hospital 5 days after onset with a good outcome.