Heterotopic ossification (HO) is the abnormal development of bone within soft tissue. It is frequently encountered after traumatic brain injury or spinal cord injury, rather than lower motoneuron disease. It has been reported as a rare complication in Guillain-Barré syndrome (GBS). We present the case of a 31-year-old woman who suffered from pain and swelling with limitation of the passive range of motion on right hip joint, and who had been diagnosed with GBS about 1 year previously. She was wheelchair-bound and had incomplete tetraplegia with flaccidity. She was diagnosed as HO based on the radiologic imaging study. She did not reveal any encephalopathy-related symptoms or signs, and hypercalcemia, and/or related metabolic derangement during 1.5-year follow-up period. Owing to the paucity of other causative factors, we presumed that the long-time hypomobility, even though not accompanied by hypercalcemia, played a major role for the development of HO. Early active rehabilitative management was initiated. The outcome is not promising because of her long-standing paralyzed state; however, it was possible to prevent the aggravation of HO.