Gelatin-based hemostatic agents are widely used in neurosurgery. This is a case of postoperative aphagia strongly suspected to be caused by an allergic reaction to a gelatin-based hemostatic agent after anterior cervical decompression and fusion for central cervical cord injury. A 55-year-old man underwent cervical anterior decompression and fusion at the C3/4 and 4/5 levels for central cervical cord injury. Immediately after the surgery, he could not swallow saliva at all, but his voice was not hoarse. Postoperative cervical computed tomography and magnetic resonance imaging showed significant edema from the post-hypopharynx wall to the front of the vertebral body. The retropharyngeal space was remarkably enlarged to 15.8 mm with cervical spine X-rays. Without neurological symptom improvement, his condition was diagnosed as marked edema of the area where Surgiflo (porcine-derived gelatin-based hemostatic agent; Johnson & Johnson Wound Management, Somerville, NJ, USA) had been applied during the operation. It was strongly suspected to be caused by an allergic response to the porcine-derived gelatin. When methylprednisolone 1000 mg was administered for 3 days from the 5th postoperative day, swallowing became almost normal within a few hours after the initial administration, and his neurological symptoms improved. The patient left the hospital on the 12th day after the operation. Before using porcine-derived gelatin products during surgery, special consideration should be given to patients with an allergy history before surgery.