The invention relates to a neurodegenerative disease treating agent for parenteral use, which comprises (2R)-2-propyloctanoic acid or a salt thereof. Since the neurodegenerative disease treating agent of the present invention comprising (2R)-2-propyloctanoic acid or a salt thereof, characterized in that a dosage exceeding about 100 mg per dose is parenterally administered, shows neuropathy improving effect and S-100 .beta. increase inhibiting effect in patients with cerebral infarction, it is useful for the treatment of neurodegenerative diseases including cerebral infarction. In addition, it is also useful as a neural regeneration agent after transplantation.