Intrathecal baclofen (ITB) therapy is an established surgical treatment for spasticity. Long-term management of ITB may necessitate catheter replacement, which typically requires a new dural puncture. Although rare, complications such as cerebrospinal fluid leakage, nerve injury, and hemorrhage can occur with a new dural puncture. We successfully replaced an intrathecal catheter of ITB through a granulation tunnel formed around the old catheter using a 16-gauge vein catheter, without the need for a new dural puncture. A 79-year-old man with spasticity resulting from cervical spinal cord infarction underwent ITB therapy and required intrathecal catheter replacement. During the replacement surgery, a 16-gauge indwelling peripheral vein catheter was inserted into the granulation tunnel around the old catheter, using the old catheter as a guide. After the old catheter was removed, the vein catheter remained in place, and a new intrathecal catheter was carefully introduced through the vein catheter. The catheter was successfully advanced into the subarachnoid space via the vein catheter and granulation tunnel, completing the procedure without any surgical complications. This technique can reduce the risks associated with dural puncture, lower radiation exposure, and decrease the overall surgical time.