Objective: To report one case of cubital tunnel syndrome due to repetitive work Method: The authors examined a worker who complained of severe muscle atrophy between the right thumb and index finger, claw deformity and numbness of the 5th finger. We evaluated him with physical examination, neurophysiologic studies (nerve conduction study, NCV; electromygraphy, EMG), plain X-ray and magnetic resonance image(MRI) at the right elbow. We also investigated his occupational history, and analyzed his work motions, using rapid upper limb assessment (RULA) of the work cycle at his previous work site. Result: The patient had been a ship welder for 17 years, followed by 6 years of dismantling boxes and loading/unloading materials. The latter job required inappropriate elbow posture such as repetitive flex-ion and extension. The NCV study revealed slow conduction velocity of the right ulnar motor and sensory nerve, decreased action potential of the right hand intrinsic muscles and flexor carpi ulnaris. The simple X-ray film showed normal finding, but MRI showed a finding compatible with cubital tunnel syn-drome combined with enlargement of the right ulnar nerve at right elbow, 0.6㎝ intraarticular loose body and medial aspect of the medial epicondyle of the right distal humerus. Conclusion: We confirmed the diagnosis of cubital tunnel syndrome that was related to his packing job which had demanded repetitive flexion and extension of elbow joint. At the time of writing, surgery was being considered as appropriate treatment.