Magnetic resonance images (MRI) of migrated nucleus pulposus after collagenase treatment of lumbar disc herniation are rarely published. Here, we describe a 65-year-old woman with L5-S1 intervertebral disc herniation on the rear left. The patient was treated with a lumbar disc collagenase injection, and the pain was relieved. Two weeks later, the patient suddenly developed pain again after engaging in weight-bearing activity. Lumbar MRI showed a nodule in the spinal canal at the L5-S1 level. The patient underwent surgical treatment two days later. Pathology showed that the nodule was nucleus pulposus tissue. Teaching point: It is important to understanding the MR manifestations of migrated nucleus pulposus after collagenase treatment to prevent such misdiagnosis.