Background Blepharoptosis is a common symptom in ophthalmology clinic, but eyelid retraction when smiling in a ptosis eye is a rare manifestation. Here we report a novel manifestation that eyelid retraction during smiling in a patient with monocular congenital ptosis.Case description A 10-year-old girl with isolated and mild unilateral congenital ptosis showed eyelid retraction in ptotsis eye when smiling together with a lid lag on downgaze. She didn't have any systematic and ocular diseases other than myopia and astigmatism.Eyelid retraction during smiling is 5 mm, resulting in a significant difference in the height of bilateral palpebral fissures.As for ptosis, is mild.The margin to reflex distance 1 is 1.0 mm on the right eye(ptosis eye) and 3.0 mm on the left eye. A lid lag of 1.0 mm on downward gaze was noted on the right, she could close her eyes fully while sleeping.The ice pack test, laboratory test for thyroid function, whole-exome sequencing (WES) and magnetic resonance imaging(MRI) of the orbital and ocular motor nerves showed normal results.Her symptoms alleviated after 6 months, with the retraction of the right upper eyelid when smiling was approximately 3 mm, thus the difference in the palpebral fissure height when smiling was smaller than that at the initial presentation.Conclusion Blepharoptosis may accompanied with abnormal innervation like eyelid retraction, this phenomenon can be alleviated with age.The results of the levator muscle function test should be carefully examined to determine whether it is ptosis in an impaired innervation eyelid.