There have been no reports of disuse syndrome in pregnant women due to hyperemesis gravidarum. In this report, we describe a case of prolonged severe hyperemesis gravidarum that resulted in disuse syndrome and required long-term rehabilitation. The patient was 28-year-old woman in her first pregnancy. She was admitted to another hospital for hyperemesis gravidarum at 9 weeks' gestation, but her symptoms did not improve and she was transferred to our hospital at 13 weeks' gestation. Central venous nutrition was started for hypofunction, and rehabilitation was initiated based on a diagnosis of disuse syndrome with marked muscle weakness caused by bed rest and immobility. Her activities of daily living gradually improved and her oral intake increased, so she was discharged home at 27 weeks' gestation. She gave birth to a baby weighing 2856 g via vaginal delivery at 38 weeks and 5 days of gestation. This case demonstrates that hyperemesis gravidarum can result in disuse syndrome due to decreased activity. In addition, undernutrition is negatively correlated with the effectiveness of rehabilitation. Thus, nutritional management is important not only for the treatment of hyperemesis gravidarum, but also for the prevention of disuse syndrome and effective rehabilitation.