Background <p>We report a case of congenital oculomotor nerve palsy presenting with aberrant eyelid movements and an involuntary pupillary reaction.</p> Case Presentation <p>A 24-year-old woman presented with mild anisocoria with no significant medical history. Her ocular history included a history of strabismus and levator muscle surgery. Examination revealed exotropia, hypotropia, and ocular motility impairment, consistent with right oculomotor nerve palsy. Pupillary examination revealed mild anisocoria with the right pupil being unreactive to dim light, followed by involuntary pupillary spasms unassociated with eye position. Twitch-like movements of the upper eyelid were also observed during the spasm phase. Orbital magnetic resonance imaging revealed atrophy of the extraocular muscles, particularly the medial rectus. No intracranial lesions were found and blood tests excluded conditions such as thyroid eye disease. Based on these findings, congenital oculomotor nerve palsy with aberrant regeneration was diagnosed. The patient remained asymptomatic and was managed conservatively. Six months later, no complications due to pupillary spasms or restriction of ocular motility were observed.</p> Conclusions <p>This case highlights an unusual pupillary response in congenital oculomotor nerve palsy characterized by involuntary pupillary spasms accompanied by upper eyelid twitching, which has not been previously reported. The prognosis was likely favorable for asymptomatic patients without associated underlying causes.</p>